




























































































































































































































































































PRACTICAL 
ELECTRIC WIRING 




PRACTICAL 

ELECTRIC WIRING 


BY 

JOHN M. SHARP 

INSTRUCTOR IN WIRING DEPARTMENT, 
BLISS ELECTRICAL SCHOOL 



ILLUSTRATED 


•> 

■» O 


REVISED EDITION 


D. APPLETON AND COMPANY 
NEW YORK LONDON 


1921 



I 







\ 

I 


I 


Copyright, 1916, 1921, by 
D. APPLETON AND COMPANY 







‘ * 


C f ( 

( 


DEC 30 1921 

©CU653308 



Printed in the United States of America 


\ 



PREFACE 


The object of this volume is to present to the student 
the practical side of electrical wiring. The endeavor 
throughout the book has been to furnish not only general 
information but sufficient special information to enable 
the student actually to install electric wiring. The sub¬ 
ject is treated comprehensively from.the method of dis¬ 
tributing current by different systems to the minute de¬ 
tails in wiring for and in installing the different fittings. 

For the wireman or electrical contractor the wiring 
tables and data will form a ready reference and some 
of the practical methods for saving time and material 
may suggest a source of increased income. 

Several important rules from the National Electrical 
Code have been given but the complete regulations have 
not been included as they may be had for the asking 
by applying to the National Board of Fire Underwriters 
in New York, Boston or Chicago. A special effort, how¬ 
ever, has been made throughout the book to comply with 
the rules contained in the 1913 edition of the code. 

The author is indebted to Professor Louis D. Bliss of 
the Bliss Electrical School for many criticisms and valu¬ 
able suggestions of an electrical nature and to Professor 
Robert J. Peters of Carnegie Institute of Technology 
for criticism and arrangement of the final copy. 


PUBLISHER’S NOTE 

In the revision of this text certain necessary changes 
have been made, and the necessary new matter has been 
included to make the volume thoroughly up to date and 
in accordance with the most recent electric wiring practice. 


VI 


CONTENTS 


CHAPTER PAGE 

I.—Introduction .i 


Importance of electric wiring—Electricians’ tools and 
their uses—Tools required by wiremen—Standard 
symbols for wiring plans. 

II. — Wire Joints and Splices .n 

Importance of good joints—Requirements for a good 
joint—Preparing wires for a joint or splice—Instruc¬ 
tions for making joints and splices—Soldering joints 
—Soldering wires into lugs—Taping a wire joint— 
Tearing friction tape. 

III. — Wiring for Bells, Annunciators, Gas Lighting . 30 

Importance of good work—Vibrating bell—Concealed 
wiring—Open work wiring—Bell wiring—Wiring for 
gas lighting—Instructions for making a good ground 
—Wiring fixtures—Multiple gas lighting—Locating 
trouble on battery systems—Sources of power for low 
voltage systems. 

IV. —Open Wiring.59 

Diagram—Execution of the work—Wood molding. 

V. —Concealed Knob and Tube Wiring .... 85 

New house—Finished house. 

/ 

VI. —Rigid Conduit.107 

Concealed and open conduit wiring—Entering the 
building—Wiring for meter—Tools used—Preparing 
conduit for use—Bending conduit—Offsets—Outlet— 
Damp places—Fireproof buildings—Grounding conduit 

vii 




viii CONTENTS 

CHAPTER 

systems—Fishing wires through conduits—Installing 
fixtures. 

VII. — Armored Cable and Metal Molding . 

Armored cable—Metal molding. 

VIII. — 'Special Wiring . 

Systems of distribution—Meter loops—Switch sugges¬ 
tions—Stairway control system—Electrolier switches 
—Burglar circuit—Remote control switches—Tank 
switches—Fittings for bathrooms and damp places— 
Locating troubles. 

IX. —Wiring Practice. 

Factors—Duties—Size of mains—Number of lights— 
Locating outlets—Knife switches—Power required for 
illumination—Wooden cabinet boxes—Insulation of 
wire. 

X. —Wiring for Motors. 

Wiring systems—'Some code requirements—Direct 
current motors—Types—Alternating current motors— 
Classes. 

XI. — Telephones . 

Important requirements—Telephone protectors—Tele¬ 
phone wiring—Caution—Kinds of telephone systems. 

Appendix. 

wiring tables. 

Conductivities—Conductors and insulators—Melting 
point and relative electrical conductivity of metals 
and alloys—Current required to fuse wires—Difference 
between wire gauges—Wire markings—Brown and 
Sharpe’s gauge—Classification of gauges—Uses of 
various gauges—Equivalents of wires; B. & S. gauge 
—Ohm’s law—Electrical units—Mils and circular mils 
—Electrical units and mechanical equivalents: am¬ 
peres per horse power, amperes per generator, amperes 
per motor. 


PAGB 


127 


146 


166 


180 


203 


225 





CONTENTS 


IX 


Appendix (Continued ) page 

wire DATA. 

Dimensions and resistance of copper wires—Galvan¬ 
ized iron wire—Fine magnet wire—Data on solid wires 
larger than 4/0 —Rubber-covered wire; solid conduc¬ 
tors—Stranded conductors—Rubber-covered duplex— 
Copper for various systems of distribution—Conduit 
sizes for different size wires. 

USEFUL TABLES. 

Metric system—Decimal equivalents—General equiva¬ 
lents—Table of multiples. 

PULLEY TABLES. 

Pulleys and gears—Rule for finding size of pulleys— 

Gear table; diametral pitch. 

Index ....... o ... . 249 






* 






PRACTICAL ELECTRIC WIRING 


CHAPTER I 
INTRODUCTION 

Importance of Electric Wiring— Electricity has be¬ 
come such an important factor in our industries and 
homes that a general education is not complete without 
some knowledge of this subject. Those who specialize in 
electricity find the field so wide and the work so varied 
that a further specialization in one of its branches must be 
made before one can hope to reach any high degree of 
success. Electric wiring is a very important branch of the 
business not only because it is essential wherever elec¬ 
trical appliances are used but because the safety of the 
buildings through which it passes depends on the charac¬ 
ter of such work. If the wiring is done according to the 
rules of the National Electrical Code and in a workman¬ 
like manner, there is little likelihood that electricity 
will cause trouble or property loss. However, where 
the Code rules are not complied with and an honest job 
is not executed, many vexatious troubles and dangers may 
arise. An attempt is not made to cover the entire field 
of electricity in this volume, but principles of electricity 
with illustrations and instructions are given to assist 
the student in becoming a practical electric wireman. 

Electricians’ Tools and Their Uses. —A wireman, 
first of all, must understand the purpose of various tools 
and know how to use them. Much time will be saved if 
the right tools are used and used properly. The follow¬ 
ing list comprises a number of tools that the wireman 

i 

O 


2 


PRACTICAL ELECTRIC WIRING 


may need, with some brief instructions as to their uses. 

The screw drivers used may be classed as cabinet, ma¬ 
chinist, ratchet and yankee. Cabinet and machinist are 
the ordinary screw drivers, the former being used for 
small and the latter for large wood and machine screws. 
The ratchet screw driver may be either large or small, 
the advantage being that it is not necessary to remove 
the driver from the screw on the backward stroke. The 
yankee screw driver, used mostly for the larger screws, 
has a spiral gear whereby the screw is turned by simply 
pushing on the handle. With any screw driver there is 
usually a tendency for the driver to twist out of the 
groove of the screw. This tendency may be overcome 
by grinding or filing off the edge squarely, making it 
conform very nearly to the shape of the groove in the 
screw. 

Pliers are made in many different styles but those most 
used by a wireman are side cutter, long-nosed, and com¬ 
bination gas pliers. The side cutter is used for cut¬ 
ting and splicing wires and general use. The 7-inch is 
the most popular length for this class of work. The 
long-nosed is used chiefly for reaching nuts, screws, etc., 
in places out of reach of the ordinary plier. The com¬ 
bination gas plier is used for turning lock nuts, bush¬ 
ings, and small pipes. 

The hammers used are nail and machinists’ ball and 
peen. Nail hammers with straight claws are sometimes 
preferred as they may be used in notching joists. The 
machinists’ ball and peen is used by the wireman for 
drilling holes in brick, concrete, etc. 

Braces should be either a ratchet or a corner brace. 
The ratchet permits boring in close places where the 
handle can be rotated only part of a turn. The corner 
brace allows faster boring in a corner. 

The bits more commonly used are bell hangers’, ships' 
auger and expansion. The bell hangers’ bit is used in 
drilling small holes usually for bell wires. The size mor* 


INTRODUCTION 


3 


commonly used is J inch by 18 inches. Ships’ auger 
car bits are used chiefly in boring joists for porcelain 
tubes. The size should be f inch by about 20 inches. 
Expansion bits have a cutter that is adjustable for dif¬ 
ferent-sized holes and are used in boring holes for con¬ 
duit, etc. A good size to employ is one capable of ad¬ 
justment from J to 1^ inches. 

Bit extensions are often used in boring deep holes with 
a short bit. The electrician usually prefers one about 
18 inches long that will follow a f-inch bit. 

Boring machines are used for boring floor joists for 
porcelain tubes. Some types allow the wireman to stand 
on one floor and drill the beams of the floor overhead. 
They are rather expensive and are not in common use. 

Saws for the electrician may be classed as compass, 
molding and hack saws. The compass saw is used for 
many purposes, though its main use is for sawing off 
floor boards in a finished house preparatory to removing 
them. Fourteen and 16-inch are good lengths for gen¬ 
eral use. Molding saws, as the name implies, are used 
for cutting wood molding. Hack saws are used chiefly 
for cutting conduit, armored cable and metal molding. 
Fine-tooth blades are preferred for this class of work. 

Chisels may be classed as wood, floor and cold. Wood 
chisels are used with saws in notching floor joists, etc. 
Half-inch is the width commonly used. Floor chisels 
have thin wide blades and are made specially for re¬ 
moving floor boards. Cold chisels are used for cutting 
iron and for drilling holes in brick, concrete or stone. 

Star drills and drill heads are more commonly used 
for drilling brick and concrete. 

The wrenches used are known as monkey or pipe. The 
monkey wrench, though not usually necessary for a wire- 
man, may be used on lock nuts and sometimes on ma¬ 
chine bolts and nuts. Stilson or other pipe wrenches are 
always necessary on a conduit job for screwing pipes 
into couplings and for other pipe work. 


4 


PRACTICAL ELECTRIC WIRING 

Pipe vises are required on a conduit installation to 
hold the conduits for cutting and threading. 

Stock and dies are used for cutting threads on the con¬ 
duit. Dies and guides for different-sized conduits may 
be used in the same stock. A stock of the proper size 
with the following size dies and guides, J, f, i and i\ 
inch, makes a good threading outfit for a wireman. 

Pipe cutters are faster than hack saws for cutting con¬ 
duits and are generally employed for the larger jobs. 

Reamers a^e for wood and iron. The wood reamer is 
used chiefly in reaming out the screw holes in wood 
molding so that the screw head will be counter sunk. 
Iron reamers of about the same size are also used in 
reaming out screw holes in metal molding. Iron or 
conduit reamers are used in reaming the burrs from the 
inside of the conduit after it has been cut. The size in 
most general use tapers from ij inches to T ^- inch. 

The files used chiefly are round or rat-tail, flat, and 
three-cornered. The round is used for reaming burrs 
from the inside of conduits. The flat is used for scrap- 
ing pipes and conduits, for ground clamps, and for sharp¬ 
ening bits, screw drivers, and other tools. The three- 
cornered is used chiefly for cutting metal molding. 

Steel fish tape is used in fishing wires through con¬ 
duits. Fifty feet is a good length for ordinary use. 

Combination squares are used in mitering wood mold¬ 
ing. 

Miter boxes or miter frames are used in mitering wood 
molding. 

Lever molding cutters are used in cutting metal 
molding. 

Drills are chiefly hand and breast drills. The hand 
drills are used for drilling screw holes in wood molding. 
The breast drills are used for drilling holes in metal, 
such as cabinet or switch boxes, for the screws that 
hold the switches or cut-outs in place. An assortment 
of twist drills should be kept on hand for drilling holes 


INTRODUCTION 


5 


in switch or cabinet boxes for wood or machine screws. 
Sizes and ^ make the right-sized hole for tapping: 
for 8-32 and 12-24 machine screws and are usually the 
most important. 

Taps are often required for tapping holes for machine 
screws in metal boxes. For supporting switches, branch 
blocks, etc., the 8-32 and 12-24 are most commonly 
used. 

* / 

A tap wrench, of course, is required for turning these 
taps. 

Splicing clamps are used for holding the larger or stif- 
fer copper or iron wires while the joint is being made. 
They are most used by the lineman; an interior wireman 
• seldom needs them. 

Torches are generally gasoline or alcohol. The gaso¬ 
line torch is used chiefly in heating the larger joints for 
soldering and in heating soldering coppers. The pint 
size is preferred because it holds enough gasoline for 
the usual job and is lighter to carry. The alcohol torclf 
is employed in soldering the smaller wires such as Nos. 

18, 14, and 12. It can be started much more quickly than 
the gasoline torch and for that reason is preferred for ' 
lighter work. 

Soldering coppers are used in soldering wire joints. 
Where it is practical they should be employed for all 
soldering instead of using a flame. The copper is safer 
and a joint so soldered is less liable to become overheated 
and cause the wire to break. 

Measuring rules for the wireman are usually the zig- 
zag type, either 4 or 6 feet in length. 

Molding cutters of the lever type are employed in 
cutting the backing and capping of metal molding. 
Lever punches are also used for cutting slots in metal 
molding from the screw hole to the end of the molding. 
Trowels of the smaller size are often required for “patch¬ 
ing up” the holes around switch or cut-out boxes. 

Wire gauges are sometimes required for gauging dif- 

1 


6 


PRACTICAL ELECTRIC WIRING 


ferent sizes of wire, though wiremen seldom find it 
necessary to use one. 

Tools Required by Wiremen. —The wireman may 
have occasion to use all the tools before mentioned but 
it would be a useless expense to buy them all outright, 
as some would seldom be required and others, especially 
the heavier ones, are frequently furnished by the con¬ 
tractor. A much better plan is to buy a few of the most 
used tools and add to the stock as conditions on the job 
require. The following list of tools makes a good out¬ 
fit for a wireman: 

i 6-inch machinist’s screw driver 
I 3-inch cabinet screw driver 
i pair of 7-inch side-cutter pliers 
I pair of combination gas pliers 
i i-lb. claw hammer 
i ratchet brace—io-inch sweep 
I ship’s auger car bit, size f by 20 inches 
1 bell hanger’s bit f by 18 inches 
1 expansive bit with range of | to i£ inches 
I hollow handle hand drill 
I 10-inch Stilson wrench 
1 14-inch Stilson wrench 
1 14-inch compass saw 
1 10-inch hack saw 
1 gasoline torch, pint size 
1 alcohol torch 
1 soldering copper, 1 i-lb. 

I set of drills and taps 
1 tap wrench 
1 8-inch mill file 
1 4-foot zigzag rule 
1 jackknife 
1 tool bag 

Standard Symbols for Wiring Plans.— The builder’s 

symbols for wiring plans, shown on the following pages, 
are used to signify the different outlets to be wired for 


INTRODUCTION 


7 


in a new building. The building contractor usually sub¬ 
mits to the electrical contractor a blue print of the plans 
of the building, using the following symbols to indicate 
the location of the outlets. The electrical contractor lo¬ 
cates the distribution centers, if they are not already lo¬ 
cated, and groups the outlets on the branch circuits. The 
branch circuit wiring is planned by drawing a red or 
white dotted line, for each branch, from the center of 
distribution to all the outlets to be included on that cir¬ 
cuit. An effort, of course, is made to use the smallest 
possible amount of wire and material and still allow no 
branch circuit to carry more than 660 watts of energy. 


STANDARD SYMBOLS FOR WIRING PLANS 

AS ADOPTED AND RECOMMENDED BY 

# 

THE NATIONAL ELECTRICAL CONTRACTORS’ ASSOCIA¬ 
TION OF THE UNITED STATES 

AND 

THE AMERICAN INSTITUTE OF ARCHITECTS 

Copies may be had on application to the Secretary of the National Electrical 
Contractors’ Association, Utica, N. Y., and the Secretary of the 
American Institute of Architects, Washington, D. C. 



Ceiling’Outlet; Electric only. Numeral in center indicates 
number of Standard 16 C. P. Incandescent Lamps. 



Ceiling Outlet; Combination, f indicates 4-16 
C. P. Standard Incandescent Lamps and 2 
Gas Burners. If gas only 




Bracket Outlet; Electric only. Numeral in center indi¬ 
cates number of Standard 16 C. P. Incandescent Lamps. 



Bracket Outlet; Combination, f indicates 4-16 
C. P. Standard Incandescent Lamps and 2 
Gas Burners. If gas only 




Wall or Baseboard Receptacle Outlet. Numeral in center 
indicates number of Standard 16 C. P. Incandescent 
Lamps. 


Floor Outlet. Numeral in center indicates number of 
Standard 16 C. P. Incandescent Lamps. 



8 PRACTICAL ELECTRIC WIRING 



Outlet for Outdoor Standard or Pedestal; Electric only. 
Numerals indicate number of Standard 16 C. P. Lamps. 



O 

cOo 

S’ 

5 2 

5 3 

5 4 


S D 

$ E 

B 


WiViV 

&>>>>> 



ESI 



Outlet for Outdoor Standard or Pedestal; Combination, 
f indicates 6-16 C. P. Standard Incan. Lamps; 6 Gas 
Burners. 

Drop Cord Outlet. 

One Light Outlet, for Lamp Receptacle. 

Arc Lamp Outlet. 

Special Outlet for Lighting, Heating and Power Current, 
as described in Specifications. 

Ceiling Fan Outlet. 

S. P. Switch Outlet. 

D. P. Switch Outlet. 

3- Way Switch Out¬ 
let. 

4- Way Switch Out¬ 
let. 

Automatic Door 
Switch Outlet 

Electrolier Switch 
Outlet. 

Meter Outlet. 

Distribution Panel. 

Junction or Pull Box. 

Motor Outlet; Numeral in center indicates Horse Power. 

Motor Control Outlet. 

Transformer. 


Show as many Symbols as there 
are Switches. Or in case of a 
very large group of Switches, 
indicate number of Switches by 
a Roman numeral, thus S l XII, 
„ meaning 12 Single Pole Switches. 

Describe Type of Switch in Speci¬ 
fications, that is, 

Flush or Surface, Push Button or 
Snap. 


Main or Feeder run concealed under Floor. 


Main or Feeder run concealed under Floor above 


Main or Feeder run exposed. 










INTRODUCTION 


9 




ft 

N 

8 





-© 

—(D 

E 



' Branch Circuit run concealed under Floor. 

Branch Circuit run concealed under Floor above. 
“““ ** Branch Circuit run exposed. 

Pole Line. 


Riser. 

Telephone Outlet; Private Service. 

Telephone Outlet; Public Service. 

Bell Outlet. 

Buzzer Outlet. 

Push Button Outlet; Numeral indicates number of 
Pushes. 

Annunciator; Numeral indicates number of Points. 
Speaking Tube. 

Watchman Clock Outlet. 

Watchman Station Outlet. 

Master Time Clock Outlet. 

Secondary Time Clock Outlet. 

Door Opener. 

Special Outlet; for Signal Systems, as described in Speci¬ 
fications. 

Battery Outlet. 

\ w 

( Circuit for Clock, Telephone, Bell or other 
) Service, run under Floor, concealed. 

I Kind of Service wanted ascertained by Symbol 
* to which line connects. 

( Circuit for Clock, Telephone, Bell or other Serv- 
' ice, run under Floor above, concealed. 

I Kind of Service wanted ascertained by Symbol 
to which line connects. 


NOTE.—If other than Standard 16 C. P. Incandescent lamps are de¬ 
sired, Specifications should describe capacity of Lamp to be used. 











10 


PRACTICAL ELECTRIC WIRING 


Suggestions in Connection with Standard Symbols 
for Wiring Plans.—It is important that ample space 
be allowed for the installation of mains, feeders, 
branches and distribution panels. 

It is desirable that a key to the symbols used accom¬ 
pany all plans. 

If mains, feeders, branches and distribution panels 
are shown on the plans, it is desirable that they be 
designated by letters or numbers. 

Heights of Centre of Wall Outlets (unless otherwise 
specified) 


Living Rooms. 5' 6" 

Chambers. 5' * o" 

Offices. 6' o" 

Corridors. 6' 3" 

Height of Switches (unless otherwise 

specified) . 4' o" 


( Copyright 1906 \ by the National Electrical Contractors’ 
\ Copyright 1907 / Association of the United States. 

Used by permission- 








CHAPTER II 


WIRE JOINTS AND SPLICES 

Importance of Good Joints. —Wire joints and splices 
are a vital feature of an installation. If the joint or 
splice is not made and soldered properly it may cause the 
wire to heat abnormally because of the high resistance 
contact, or if the joint makes loose contact it may produce 
an arc which, if near inflammable material, will set fire 
to the building. For these reasons much care should be 
used in splicing wires or making joints for branches car¬ 
ried from them. 

Requirements for a Good Joint. —The following are 
the requirements for a good joint or splice: 

1. It must be as strong mechanically as the wire it¬ 
self. 

2. It must have as great a conductivity as the wire, 
otherwise it would be liable to become excessively heated 
by the passage of the current through it. 

3. It should be so secure that,the wires cannot be 
worked back and forth, thereby making a loose-fitting 
contact. 

4. It should be neatly made and as small as possible, 
consistent with the observance of the preceding require¬ 
ments. 

5. It must be as well insulated as the wires which it 
joins. 

In the 1913 edition of the National Electrical Code 
the requirements for wire joints and splices are as fol¬ 
lows : (16— C) The wires “must be so spliced or joined 
as to be both mechanically and electrically secure with¬ 
out solder. The joints must then be soldered unless 

II 


12 


PRACTICAL ELECTRIC WIRING 


made with some form of approved splicing device and 
covered with an insulation equal to that on the conduc¬ 


tors.” 


Preparing Wires for a Joint or Splice. —In preparing 
the wires for a joint the insulation should be removed 
for from 3 to 10 inches of the length, depending on the 
size of wire used. The insulation should be removed with 
a knife, care being taken not to nick the wire. In re¬ 
moving the insulation the knife blade should be passed 
into the covering almost parallel to the wire as shown in 
Fig. 1 A. The insulation should not be cut with the 
knife blade at right angles to the wire as shown in Fig. 
iB, for in doing so one is likely to cut the wire so deeply 
that it will break later. 



B 


A 


Figure i. 


After the insulation is cut off, the wire must be 
scraped till it is clean and bright. This not only insures 
good electrical contact between the wires but is very 
necessary where the joint is to be soldered. In scraping 
the wire clean of impurities the cutting edge of the knife, 
of course, may be used, but a much better plan is to use 
one of the square or right-angle edges at the back of the 
blade for this purpose. The foregoing general instruc¬ 
tions for preparing the wire for joints or splices may be 
used for all wires. 

Instructions for Making Joints and Splices. —With 

the following instructions for making wire joints or 
splices some uses of the joint or splice in practice will 
be given. 

Western Union Splice .—The Western Union splice is 
by far the most widely used splice. Though its greatest 
use is with small wires it may be employed with large 






WIRE JOINTS AND SPLICES 


13 


solid wires with the aid of splicing clamps and pliers. It 
is used almost exclusively for making splices in interior 
wiring for bells, lights and motors. Also in outside work 
most of the joints that are made in solid wires are West- 




Figure 2. 


ern Union. There are two types of the Western Union 
splice, namely, the long tie and the short tie, the main 
difference in these being in the length of the twist be¬ 
tween the wrappings. As the names indicate, the short 
tie has a short twist between the wrappings, while the 
long tie has a long twist which is sometimes made with 
a pair of connectors or splicing clamps. 




























14 


PRACTICAL ELECTRIC WIRING 


To make the short tie Western Union splice use two 
pieces of No. 14 wire and scrape off about 3 inches of 
the insulation as previously described. Cross the wires 
as shown in Fig. 2A and twist by holding the lower 
part of the cross with the hands and pushing the point b 
from you and pulling a toward you. 

Then hold the twist with the pliers at the point c in 
Fig. B and wrap the wire d round e for at least five 
turns, making the wrappings fit snugly up against the 
wire e. Next grip the splice at the point f, Fig. 2C, and 



B 

Figure 3. 

wrap h round g for five or six turns, making a finished 
joint as shown at D. The ends of the wrapping wire 
should be cut off close to the main wire and the end 
pressed in against the main wire to prevent piercing the 
tape with which the splice is to be wrapped. From 
inch to 1 inch of bare wire should be left between the 
joint and insulation to avoid burning the insulation when 
the joint is soldered. 

The long tie Western Union splice made with small 
wires, shown in Fig. 3A, is made in the same manner 
as the short tie, the only difference being that a longer 
twist is made in the wires before the wrapping is begun. 
The advantage claimed for the long tie over the short tie 
is that the twist between wrappings allows a better 
chance for solder to pass in between the wires. 

To make a long tie Western Union splice with large 
wire, the wires are held together by splicing clamps and 





















WIRE JOINTS AND SPLICES 


15 


one wire is wrapped round the other on both sides of the 
clamp. Pliers are used for this purpose when the wires 
are too stiff to be wrapped with the hand. Fig. 3B shows 
a splice made in this manner. 

Tee Joint .—The tee joint is used in making a branch 
or tap-off from an existing line of wiring. It is used 
in interior; wiring for bells, lights, and motors, and also 
in outside work where solid conductors are used. There 
are two tee joints, the plain tee and the loop tee. The 
plain tee shown in Fig. 4A is made by wrapping the 
end of the branch or tap wire round the installed con¬ 
ductor. 

Loop Tee Joint .—The loop tee shown in Fig. 4B is the 
same as the ordinary tee except that a loop is made be¬ 
fore the wrapping is begun. To make the loop tee joint, 
pass the wire a in Fig. 4B round the wire b, then pass 
it across the wire a and wrap it round the wire b in 
the opposite direction from the way it was started. For 
small wires this joint is considered much better than the 
ordinary tee because the loop prevents the wire from 
unwrapping under strain. 

When it becomes necessary to run a double branch 
circuit, that is, a branch circuit each way, from a line 
of wiring, the joints shown in Figs. 4C and D make neat 
and also good electrical and mechanical connections. In 
Fig. C the crossing wire is cut and two tee joints are 
made with the first layers of the wrappings of each joint 
lying adjacent. In Fig. D the crossing wires are bared 
of their insulation and a short piece of wire of the same 
size is wrapped round both of them for five or six turns. 

Three-ply Splice .—The three-ply joint, though not 
often used in practice, is an excellent joint where extra 
mechanical strength is desired. To make this joint an 
extra wire is placed parallel to one of the wires as shown 
in Fig. 5A and a twist is made in the same manner as the 
twist for the short tie Western Union joint. Then the 
wires at c are wrapped together round b for five or six 



WIMffl 


<□ 


A 




m$m=cni 


a 


B 




Figure 4. 



















































WIRE JOINTS AND SPLICES 


17 


turns. The extra wire at a is then pulled parallel to d 
and the two wires are wrapped round a, making the 
joint shown in 5B. 

Rat-tail Joint .—The rat-tail joint is used almost en¬ 
tirely in joining wires at junction or outlet boxes in a 




conduit system. This joint is not very strong mechan¬ 
ically and should not be used where there is any strain 
on the wire, but for a junction or outlet box where there 
is no strain on the joint it is equal to any other electri¬ 
cally and is much more easily made. To make this joint 
the wires are crossed, lying almost parallel to each other 
and twisted together as shown in Fig. 6A. 

As shown in the figure only two wires are included 

























i8 PRACTICAL ELECTRIC WIRING 

in the twist, though almost any number may be joined 
in the same manner. 

Fixture Splice .—When a fixture wire which is usually 
size 18 is to be joined to a branch circuit wire which is 
size 14 or larger, the joint is made similarly to Fig. 6B. 
The smaller wire is wrapped round the larger wire for 






several turns, then the end of the larger wire is bent 
back over the joint and the smaller wire is wrapped round 
the joint and the bent back portion of the wire for a few 
turns. This hook in the large wire prevents the wrap¬ 
pings made by the small wire from slipping off the end of 
the larger wire. 

Britannia Splice .—The Britannia splice is used in out¬ 
side line work or anywhere that large solid wires are 
to be joined. Though it is not so popular as the long 
tie Western Union joint, it makes an excellent splice 
when properly made and soldered. In the Britannia 






WIRE JOINTS AND SPLICES 


19 


splice the wires, which have been previously cleaned of 
their insulation for about five inches, have about a half¬ 
inch of the ends turned at right angles to the wire. As 
shown in Fig. 7 the right-angled turns should be made as 
sharply as possible and the surface of the two wires 
should fit snugly when held together. 

For a No. 6 or 8 wire allow about 4 inches for the 
joint and prepare 5 or 6 feet of No. 18 for the wrapping 



ix_n 





s' r 1 


u 




wire. Hold the wires together with a pair of pliers or 
connectors and beginning at the middle of the joint and 
also the middle of the small wire, wrap the small wire 
round the two wires to the end of the joint and for a few 
turns on the single wire. The joint is then turned about 
and the other half of the small wire is wrapped round 
the other portion of the joint in a similar manner. 
Lastly, the ends that are turned up are cut off close to 
the joint. 

Tdper Cable Splice .—There are several methods of 
joining stranded wires, but the taper cable splice is so 
much superior, both electrically and mechanically, to all 
the other splices known to the writer that the in- 















20 


PRACTICAL ELECTRIC WIRING 


structions for making it will be given. To prepare the 
wire for the joint the insulation should be removed from 
the cable from 6 to io inches, depending on the size of 
the wire. Then each wire of the strand should be drawn 
back and scraped until it is clean and bright. The core, 
which is the wire or wires in the center of the cable, 
should have about two-thirds of its length cut off and 
the remaining wires twisted together as in the original 
core, and then all strands should be put back as they were 
before cutting the core, doing this as far as the end of the 
core. At this point the outer wires should be bent back 
almost at right angles to the cable as shown in Fig. 8A. 

After the other cable of the splice has been prepared 
in a similar manner the wires of the two cables are 
meshed together as shown in Fig. B. The wires from 
cable a are pressed down on cable, b and the wires from 
cable b are pressed down on cable a as shown in Fig. C. 
Then one of the wires is wrapped round all the conduc¬ 
tors as shown in Fig. C. Another wire is drawn up near 
the end of this wire and passed round all of the remain¬ 
ing wires. This operation is kept up until all the wires 
on that side of the joint have been passed round the 
cable. The other end wires are treated in the same man¬ 
ner, presenting a finished splice shown in Fig. D. To 
make the splice look neat the overlapping wires should 
form a round surface for the wrappings and the last 
wire used in wrapping should be made to end, usually 
by cutting it off, at the point where the next wire starts. 
This splice is called the taper cable splice because it tapers 
from the middle toward each end. 

Tee Joint for Stranded Wire .—A tee joint made with 
stranded wire is usually made as shown in Fig. 9. After 
the wires have been cleaned of their insulation and pre¬ 
pared for the joint, the strands of cable a are divided 
equally and are spread out V-shaped to fit over cable b 
as shown in Fig. 9A. Then all the wires of the right- 
hand section are passed together round the cable in 





fi 

Figure 8 


21 


































































































22 


PRACTICAL ELECTRIC WIRING 


one direction and all in the left-hand section are passed 
round the cable in the other direction. The finished 
joint is shown in Fig. 9B. 




When it becomes necessary to splice two wires that are 
braided or twisted together, such as duplex or twisted 
lamp cord, the joints should be staggered as shown in Fig. 
10. This not only makes a neater looking job but avoids 
the possibility of the wires becoming short-circuited 
through the tape at the joints. 


















































WIRE JOINTS AND SPLICES 


23 ' 


Soldering Joints. —All the joints and splices previ¬ 
ously described, if used in interior wiring, must be 
soldered and taped. In wiring for bells and annunciators, 



or other instruments where the voltage is low, there are 
no Code requirements and, except in rare cases, the joints 
are not soldered. 

The three most popular methods of soldering joints 
are with a gasoline torch, an alcohol torch, or a solder- 



C 

Figure ii. 















































24 


PRACTICAL ELECTRIC WIRING 


ing iron, which are shown in Figs. 11A, B and C respec¬ 
tively. Each one is adapted to a particular kind of work, 
though where the heat furnished is sufficient, they may 
be used interchangeably. ' The gasoline torch furnishes 
the largest flame and is adapted to soldering large wires, 
to sweating wires into lugs, or to heating a soldering 
copper. The alcohol torch is adapted to soldering only 
the smaller wires such as joints made in sizes Nos. 18, 14 
and 12. Though it does not furnish enough heat to 
solder the larger wire, it has a great advantage over the 
gasoline torch in that to prepare it for soldering it is only 
necessary to light it. The soldering copper is adapted 
to use where a flame is objectionable, as on the wall of 
a room or between floors. 

Gasoline Blowtorch .—To start a gasoline blowtorch 
proceed as follows: First, select a place where there is 
no material that burns readily and where the black smoke 
from the gasoline is not objectionable. This operation 
should be done out of doors but the torch must be 
shielded from the wind or it will not heat properly. Sec¬ 
ond, put pressure on the gasoline by working the pump 
until it becomes rather hard to pump. Third, holding the 
hand over the end of the burner, open the needle valve 
and allow gasoline to flow down and fill the container 
under the burner. Fourth, with the needle valve closed, 
touch a lighted match to the gasoline in the container 
which, if allowed to burn up, will heat the burner to 
working temperature. Fifth, open the needle valve and 
hold a lighted match to the end of the burner; if a blue 
flame is produced, the torch is ready for use. 

Sometimes even after this process the flame produced 
is not blue, which fact indicates that the burner has not 
been heated sufficiently to vaporize the gasoline. The 
burner may be brought to working temperature by apply¬ 
ing the flame to the ground or some metallic surface and 
allowing the heat from the flame to rise and heat the 
burner. 


WIRE JOINTS AND SPLICES 


25 


To solder a joint with a gasoline torch, first apply 
a soldering paste over the entire joint. Next hold the 
joint in the flame and when it is hot enough to melt 
solder apply solder over it for the entire length of the 
joint. The solder must be sweated in between the wires, 
which is generally indicated by the smooth surface of 
the solder covering the joint. 

When using a gasoline torch one should use much 
care to prevent overheating the wires, which may result 
in either of two things. If the joint gets too hot before 
the solder is applied the solder will not adhere to it. The 
solder may adhere before the joint is overheated, but 
overheating the wires makes it so brittle that it is liable 
to break after it is put into service. 

Alcohol Torch .—In soldering with an alcohol torch the 
flame from the wick is blown upon the joint and the joint 
is soldered as with a gasoline torch. 

Soldering Copper .—To solder a joint with a soldering 
copper the copper should be heated until it will melt 
solder quickly. It is then held against and preferably 
under the joint which has been covered with soldering 
paste and as the joint becomes heated the solder is 
applied. 

Tinning Soldering Copper .—Before a soldering copper 
is used it must be thoroughly tinned; that is, the sides at 
the point must be covered with a film of solder. To tin 
a soldering copper the copper is heated until it will melt 
solder, and the surface at the joint is filed or sand-papered 
dean. Then solder which has a small amount of paste 
clinging to it is applied to the point. This should form 
a film of solder over the point of the copper. If the 
solder fails to adhere, it is probably due to a dirty sur¬ 
face or to the copper’s being overheated. If, when filing 
the copper, the surface turns blue, this fact indicates that 
the copper is too hot and solder will not adhere until 
the copper has been cooled and the surface refiled. After 
the copper has been tinned each time it is taken from the 


26 


PRACTICAL ELECTRIC WIRING 


heat preparatory to soldering, the surface should be 
wiped with a piece of waste or a rag. In the use of a 
soldering copper many electricians tin only one side 
which, when the copper is held under the wire, prevents 
the solder from spreading to the other sides and dropping 
to the floor. Another excellent plan for soldering wires 
with a copper is to cut a groove across one side of the 
point, as shown in Fig. 12, into which the wires are 
placed for soldering. 

If only the inside of the groove is tinned the joint 



may be placed in the groove and solder applied until the 
joint is partially or wholly covered with molten solder. 

Summary .—As a summary, the following brief instruc¬ 
tions should be followed in soldering joints: 

1. Thoroughly clean the wires; 

2. Apply soldering paste freely; 

3. Heat, but do not overheat the joint; 

4. See that solder covers the joint, is thoroughly 
sweated in, and presents a smooth surface. 

Soldering Wires into Lugs. —The Code states that all 
wires whether stranded or solid, when they have a con¬ 
ductivity greater than that of No. 8B & S gauge, must be 
soldered into lugs for all terminal connections, except 
where an approved solderless terminal connector is used. 
Unless these wires are properly soldered into the lug the 
wire may pull out when in service, or the high resist¬ 
ance of the poor contact may cause the joint to heat. 

The most common way of sweating wires into lugs is 
with a gasoline blow-torch. The wire should be scraped 








WIRE JOINTS AND SPLICES 


27 


clean of insulation far enough back from the end to allow 
the wire to reach the bottom of the lug when inserted. 
The lug is held in the flame of the torch and as it heats 
soldering paste is inserted into the lug followed by solder 
which is fed in until the lug is about three-fourths full. 

The wire to be inserted should first be covered with 
soldering paste and then tinned. To tin the wire immerse 
it in the molten solder in the lug and after a few seconds 
take it out and see if a thin film of solder covers the wire. 
If the surface is not covered with solder the operation 
must be repeated until the wire is thoroughly tinned. 



Figure 13. 


After the wire is tinned it may then be inserted into the 
lug and then both are allowed to cool. The lug may be 
cooled much quicker by applying it to some wet waste. 
The wire should never be plunged into the lug before it 
has been tinned or before it has been heated to a tem¬ 
perature near that of molten solder. If in this process 
the lug has been blackened by the flame it may be cleaned 
with sandpaper. 

Taping a Wire Joint. —In wiring for lights and 
motors all joints must be taped with either friction tape 
or rubber and friction tape both. In open wiring where 
weatherproof wire is permitted friction tape is approved 
for taping the joint. In all other systems of interior 
wiring both rubber and friction tape are required. In 
all systems the insulation formed by the tape must be 
equal to the insulation on the wire; therefore, as the joint 
has a larger diameter than the wire, the taped joint will 
be a little more bulky than the insulation. 




28 


PRACTICAL ELECTRIC WIRING 


To tape a joint with friction tape begin at the insula¬ 
tion and wrap the tape spirally round the joint and bare 
wire, making each succeeding convolution overlap the 
preceding one from one-half to two-thirds the width of 
the tape, continuing the operation back and forth until 
the insulated joint has a diameter a little larger than the 
insulated wire, as shown in Fig. 14. 

Where rubber and friction tape are used together the 
rubber tape is placed next to the wire as the insulation 
and the friction tape is wrapped over it as a binder. The 
rubber tape should be tightly wrapped round the wire 



Figure 14. 


making an insulation of thickness equal to that of the 
rubber covering of the wire. This rubber may be vulcan¬ 
ized upon the wire by applying heat from a lighted match 
or by grasping it with the hand for a short period of 
time. Friction tape is then wrapped round the rubber 
tape, forming a finished joint as shown in Fig. 14. 

Tearing 1 Friction Tape. —If, in wiring, a man uses 
methods of separating friction tape other than tearing 
it with his fingers, he is considered a novice by experi¬ 
enced men. If the tape is held firmly in the hands and 
given a quick pull, causing the strain to come on one 
edge, it will tear very easily. As a convenience leave one 
inch or two of tape between the roll and the place where 
it is torn off. 


QUESTIONS. 

1. What dangers may arise from a poorly made joint? 

2. What are the requirements for a good joint? 

3. Describe the method of preparing wires to be joined, 
f. Where is the Western Union splice used? 









WIRE JOINTS AND SPLICES 


29 


5. What is the difference between a short and a long tie 

Western Union joint? 

6. Describe in detail the method of making a short tie 

Western Union splice. 

7. Describe the method of making the long tie Western 

Union splice in large wire. 

8. Where is the tee-joint used? 

9. Describe the method of making: (a) The ordinary 

tee; (b) The loop tee. 

10. Explain two methods of making the double tee joint. 

11. Where is the rat-tail joint used, and how is it made? 

12. How is the fixture joint made? 

13. (a) Where is the Britannia splice used? 

(b) How is it made? 

14. Describe in detail the method of making the taper cable 

splice. 

15. Explain the method of making a tee joint with stranded 

wire. 

16. Explain the method of making joints in duplex wires. 

17. On what systems must joints be soldered? 

18. In soldering wires, where is each of the following best 

adapted for use? (a) Gasoline torch? (b) Alcohol 
torch? (c) Soldering copper? 

19. State in detail the method of starting a gasoline blow¬ 

torch. 

20. Explain in detail the method of soldering a joint with 

a gasoline torch. 

21. In soldering with a gasoline torch, what must be guarded 

against ? 

22. Describe a method of tinning a soldering copper? 

23. Make two practical suggestions in the use of the solder¬ 

ing copper. 

24. Describe a method of soldering wires into lugs. 

25. Where may friction tape alone be used, and where must 

rubber and friction tape both be used in taping a 
joint ? 

26. Describe the method of taping a joint with both rubber 

and friction tape. 


CHAPTER III 

WIRING FOR BELLS, ANNUNCIATORS, GAS LIGHTING 

General Rules. —The National Electrical Code does 
not prescribe how wires for bells, telephones, annunci¬ 
ators and similar appliances shall be run except with 
relation to keeping them separate from lighting and 
power circuits. Such signal circuits as they are called 
must never be run in the same conduits or tubes with 
light and power wires and should at all places be kept well 
separated from them. 

In general current for bells, etc., should never be taken 
from the lighting circuit of a building except where an 
approved transformer is used (bell-ringing transformer). 

Electric gas lighting, except the so-called frictional 
system, should not be used on the same fixture with 
electric light. 

All signal wiring should be just as well done electri¬ 
cally and mechanically as work for electric light and 
power. 

Vibrating Bell .—One of the most common devices 
used in low voltage wiring is the vibrating bell shown in 

Fig. IS- 

In the operation of this bell the wires from the bat¬ 
tery and buttons, or other fittings, are connected to the 
binding post “a” and “a'.” The current passes in at contact 
“a,” flows through the coils through the adjusting screw 
“c,” and through the armature spring “d,” and comes out at 
binding post “a'” to line. The current passing through the 
coils causes their cores to be magnetized, which fact 
draws the armature d against these cores. This move¬ 
ment of the armature opens the circuit at the contact 
between “c” and “d,” causing the coils to be demagnetized, 
and the armature is forced back by the spring at “f.” This 

30 


BELLS. ANNUNCIATORS, GAS LIGHTING 31 


operation is repeated as long as the current continues to 
flow through the bell. The circuit being continually 
opened and closed at the contacts between c and d pro¬ 
duces a small arc. To prevent this arc from oxidizing 
the contact points, they are tipped with some non-oxi- 
dizable metal, such as German silver, silver, platinum or 
platenoid. The contact screw c may be adjusted to give 
different lengths of stroke of the armature. The spring 
at f may be adjusted for batteries of different strength. 



Figure 15. 


Concealed Wiring. —Low voltage wiring is both con¬ 
cealed and open. In a new house all the wiring should 
be concealed; this also makes a neater job in a finished 
house but it is not always possible. The best method of 
running the wires concealed is to pass them through a 
rigid conduit. The conduit is laid in the process of con¬ 
struction of the building and the wires are pulled through 
after the building is completed. Conduit raceways for 
the wires are used in fireproof buildings, but they are 
very desirable in frame buildings where there are a large 
number of wires. Bell wire may be used in the con¬ 
duits, but it is usually advisable to use a better insulated 
wire such as a rubber-covered fixture wire or the regular 
lighting wire No. 14? single-braid rubber-covered. 










32 


PRACTICAL ELECTRIC WIRING 


Usually in buildings of frame construction such as 
residences, the wires are run on the framework while the 
house is being built. In carrying the wires across joists 
holes are drilled in the joists and the wires are bunched 
together and passed through these holes. In running 
parallel to joists or studding the wires are either secured 
separately under staples or are taped into a cable and the 



cable held with a cleat. Wires with different-colored in¬ 
sulations are usually used in cables to simplify connec¬ 
tions. 

* 

Open Work Wiring.— In doing open work wiring 
the work should not only be done well electrically and 
mechanically but it should look neat. After connecting 
the wires under binding screws each wire should be 
passed around its screw to the right so that tightening the 
screw will tend to pull the wire in nearer the screw in¬ 
stead of pushing it away. Only one wire should be 

















BELLS, ANNUNCIATORS, GAS LIGHTING 


33 


fastened under a binding 1 screw—if necessary make a 
joint instead of placing two wires under a binding post. 

A coil should be made in the wires where they con¬ 
nect to the bell or other instruments and at the battery 
as shown in Fig. 16. 

The coil is made by wrapping the wire around a pen¬ 
cil five or six times. The coil adds to the appearance of 
the job and is a ready help should extra wire be needed. 

Staples should be placed over the wires at intervals of 
every four or five feet. Joints are not usually soldered 
but should be taped with friction tape. The taped joint 
should be only slightly larger than the insulated wire. 

C - - g g= — - 


Figure 17. 

Using only half the width of the tape will assist the work¬ 
man in making the joint small and neat. Each wire lead¬ 
ing out from a joint should be held by a staple to take 
the strain off the joint. The wires should run parallel 
and turns should be made at right angles to give a neat 
appearance. The wires may be run any desired distance 
apart, but where they are run side by side the same 
staple, unless it has an insulated saddle, should not cover 
two wires as the metal of the staple may short-circuit the 
wires. Where wires are run near each other the staples 
should be “staggered,” as shown in Fig. 17, and not 
placed side by side, as the staple points may touch each 
other in the wood and make a short circuit. 

Wires often have kinks which prevent their lying flat 
against the surface wired over. To straighten the wire 
secure one end and holding the wire in the hand pass 
over the wire with some pressure something smooth such 
as the side of a hammer handle. 

To cross one wire over another the top wire should 
be taped with three or four layers of friction tape and a 










34 


PRACTICAL ELECTRIC WIRING 


staple placed over each end of the taping to prevent its 
sliding along the wire. 

Often in open work wiring in a room it is desirable to 
run the wires so that they will be inconspicuous. This 
may be accomplished in many instances by running the 
wires side by side on the top of the baseboard and along 
the side of window and door facings. Also, the wires 
used may have an insulation of the same color or near the 



Figure 18. 


color of the surface wired over, which makes them less 
noticeable. 

Bell Wiring .—In the operation of bells the most 
common arrangement is to place some circuit-closing 
device, such as a push button, in the circuit, so that when 
the button is pressed the current will flow from the bat¬ 
tery through the button to the bell or bells. 

Where a number of bells are to be operated simul¬ 
taneously they may be connected in series or in multiple. 
Generally bells operate better in multiple than in series. 
With bells in series very poor results will be obtained 
unless one bell is used as a master and all the other 
bells are made single stroke. This is accomplished by 
placing a short circuit round the make and break con¬ 
tacts on all the bells except one. Then the master bell 












BELLS, ANNUNCIATORS, GAS LIGHTING 


35 


makes and breaks the circuit for all the bells and they 
vibrate together. Placing bells in series adds more re¬ 
sistance to the circuit and more cells of battery are re¬ 
quired to operate them than would be required for a 
multiple arrangement. 

Simple Door Bell .—In bell wiring the simplest arrange¬ 
ment of connections for a door bell is as shown in Fig. 
18 where the bell, battery and button are all in series. 

Door Bells with an Annunciator. —Fig. 19 shows an 



Pujh # l 


Figure 19. 

arrangement of two buttons, two bells, and a two-drop 
annunciator, adapted for a basement floor house. The 
pushing of button No. 1 causes current to flow from the 
battery through the button and back through the an¬ 
nunciator and bell No. 1, ringing bell and pulling the 
hand over to No. 1 point on the dial. Pushing button 
No. 2 causes current to flow from the battery through 
bell No. 2, annunciator, and bell No. 1. This rings both 
bells, of course, and pulls the drop over to point No. 2 
on the annunciator. The hand of the annunciator, which 
is soft iron, hangs near the iron core of the two coils 
at 1 and 2. When the current is passed through these 
coils it causes the iron core to be magnetized, which in 
turn attracts and holds the pointer. 






















36 


PRACTICAL ELECTRIC WIRING 


Two Bells and Buzzer. —Fig. 20 shows an excellent 
plan of wiring a residence for two door bells and a 
buzzer for the dining-room. The buzzer and both bells 
are usually located in the kitchen and the bells are dif¬ 
ferently toned so that the sound indicates from which 
door the call comes. 

Bells in Multiple. —Fig. 21 shows the wiring for the 
operation of bells in multiple. Other bells may be added 


Fro/if c/oor be// Ft ear c/oor Jbe// 



by connecting them across the upper and the middle 
wires. More buttons may be added by connecting them 
across the upper and the lower wires on the left side of 
the battery. 

Bells in Series. —Fig. 22 shows the wiring for bells in 
series. More bells may be added by opening the circuit 
wires and connecting them in series with the others. 
Other buttons may be added by connecting them across 
the wires to the left of the bells. 

In this arrangement the “make” and “break” contacts 
on two of the bells should be short-circuited as was pre- 




























BELLS, ANNUNCIATORS, GAS LIGHTING 37 


viously explained. Because of the extra resistance en¬ 
countered by placing bells in series a few more cells of 



battery are required than would be necessary for the same 
number in multiple. 

Return Call Systems. —Figs. 23 and 24 show two return 
call systems; that is, the home button will ring the dis¬ 
tant bell and the distant button will ring the home bell. 



In Fig. 23 only one set of battery is employed but three 
wires are required between the two locations. 

In Fig. 24 only two wires are employed between the 
two stations, but two sets of battery and double contact 
push buttons are required. In connecting the double 














































3§ 


PRACTICAL ELECTRIC WIRING 


contact push buttons the line wire is connected to the 
strap or spring in the button, the bell wire is connected 
to the upper contact, and the battery wire connected to 
the lower contact. In using either of the foregoing dia- 



ft 


— 



Figure 23. 


grams often one of the wires between the two stations 
may be eliminated by using a water pipe, gas pipe, or 
other metallic connection between the two points. 

Open Circuit Burglar Alarm System. —Fig. 25 shows 
an open circuit burglar alarm system; that is, one in 
which the circuit is normally open. The figure at the 
left is a window spring which is mortised into the win- 















BELLS, ANNUNCIATORS, GAS LIGHTING 39 


dow-facing so that when the window sash is raised the 
spring will be depressed and the closed circuit will ring 



the bell. The device shown at the top of the figure is a 
constant ringing device called an automatic drop. When 



the circuit is closed at the window spring, the current 
flows from the battery through the spring and through 
the coils in the drop and back to the battery, causing the 
armature of the device to be drawn forward, releasing 





















































40 


PRACTICAL ELECTRIC WIRING 


the drop and allowing it to fall and close a local circuit 
through the bell and battery. The bell will of course 
ring until the drop is reset even though the window be 
lowered immediately. 



Closed Circuit Burglar Alarm System. —Fig. 26 shows 
a closed circuit burglar alarm system; that is, one in 
which the circuit is normally closed. The fitting shown 
at the bottom of the figure is a door spring which is 
mortised in the door frame on the hinge side. When the 
door is closed the circuit is closed at the spring and cur- 
rent is flowing through the spring and bell, but the cur- 













BELLS, ANNUNCIATORS, GAS LIGHTING 41 


rent is carried out from the screw of the make and break 
of the bell and the armature is held against the magnets 
so that the bell does not ring. When the door is opened 
the circuit is broken at the spring which causes the. arma¬ 
ture of the bell to fall back after which the bell operates 
as a vibrating bell. The battery switch shown in the 



figure is used to shut off the battery current in the day¬ 
time or when the system is not in use. The chief advan¬ 
tage of this system is that should the wires leading to 
the spring be opened in any way the bell will ring. The 
battery used with this system should be some closed-cir¬ 
cuit type, such as the Gravity or Gordon cells. 

Simple Annunciator .—The wiring for a simple annun¬ 
ciator is shown in Fig. 27. There is a wire for every 
drop and a common battery wire. The two wires that 
connect into the button always come, one from a drop 
and the other from the battery. The wires that pass into 















































42 


PRACTICAL ELECTRIC WIRING 


the annunciator should be grouped into a cable as shown 
in Fig. 27. 

There are two types of annunciators in use, the gravity 
drop and the needle annunciator. In the gravity drop 
type there is a coil of wire wound round an iron core 
at each drop opening. When the button for this coil is 
pushed the current flows through the coil and attracts 
its armature which trips the drop and causes it to fall. 
The needle type has a coil near the needle which attracts 
the soft iron needle when current is passed through the 
coil. These needles are made of soft iron and it is 
generally taken for granted that they do not retain enough 
magnetism to show polarity, but often in practice such 
is not the case. For instance, if the current is sent in 
one way through the coil the needle will be attracted, 
but if the current is sent in the other direction through 
the coil the needle will be repelled. This plainly shows 
that the needle has developed a strong polarity. The 
needles of old annunciators usually possess more mag¬ 
netism than those of new ones, though in either case the 
magnetism may be strong enough to keep the needle from 
being attracted when the current is passing through the 
coil in the wrong direction. Usually in testing an annun¬ 
ciator of this kind, if the bell rings and the pointer is 
not attracted, reversing of the battery will cause the 
pointer to be attracted. If then the drops fail to operate, 
it is usually necessary to renew the cells or add more 
cells to the battery. New annunciators of this type have 
the common connection marked positive or negative or 
“connect zinc here,” so as to insure the right connection. 

Return Call Annunciator .—The wiring for a return 
call annunciator is shown in Fig. 28. This system re¬ 
quires one more common wire than the simple annun¬ 
ciator, also two double contact push buttons and a bell 
in each call circuit. 

When the double contact push button No. 1 is pressed, 
the upper contact is opened and the lower contact is 


BELLS, ANNUNCIATORS, GAS LIGHTING 43 


closed, causing the current to flow from the battery up 
through the button, down through the drop, through the 
push button in the annunciator and down through the bell 
to the battery. When the double contact push button No. 



Figure 28. 



































































44 


PRACTICAL ELECTRIC WIRING 


9 

I in the annunciator is pressed, the upper contact is 
opened and the lower contact is closed, causing the cur¬ 
rent to flow from the battery up through the button, drop, 
and bell No. i, passing back to the battery by the common 
bell and battery wire. 

Wiring for Gas Lighting.—In buildings gas is often 
lighted, or controlled and lighted, by electricity. In resi¬ 
dences the pendant and automatic burners are more com- 



6 



Figure 29. 


monly used in connection with a battery and spark coil, 
while in large rooms such as auditoriums or theaters 
jump spark burners are used in connection with an induc¬ 
tion coil and battery, or a static machine. 

Pendant Burner .—The pendant burner shown in Fig. 
29 has a lever which, when pulled down, opens the gas 
cock and closes and opens a contact through a battery 
and spark coil, producing a spark in the path of the 
gas sufficient to light it. The lever is pushed back to 
the original position to extinguish the gas. The spark 
produced by opening the battery circuit alone would not 
be of sufficient intensity to ignite the gas but by adding a 
spark coil an arc of much greater length is produced 
due to the self-induction of the coil. The spark coil gen¬ 
erally used consists of a bundle of iron wire 8 inches long 
























BELLS, ANNUNCIATORS, GAS LIGHTING 45 


by f inch in diameter, round which from four to six 
layers of No. 18 magnet wire are wound. 

Automatic Burner .—The automatic gas burner, as 
shown in Fig. 30, has two separate circuits through it. 
When current is passed through one set of coils an 
armature is raised which opens the gas cock and at the 






same time opens and closes the circuit at the gas tip which 
ignites the gas. Current flowing through the other set of 
coils causes their armature to be raised, which closes the 
gas cock. As shown by the wiring diagram, Fig. 31, the 
gas pipe is used as one side of the circuit for both pendant 
and automatic gas burners. 

Fig. 32 shows the wiring for a stairway control of 
two automatic burners; that is, with two burners and 
two button plates, one on each floor; either burner may 


















































































































4 6 


PRACTICAL ELECTRIC WIRING 


be lighted or extinguished from either floor. From four 
to six cells of battery are required for such a system, 
the Leclanche wet cells being generally used. 

Although the voltage of such a system is considered 
low, it soars to considerable height when the circuit is 
broken and for this reason the wires should be well in¬ 
sulated from each other. Annunciator wire is commonly 



Figure 31. 


used but much more satisfactory results are obtained by 
using a better insulated wire such as office or rubber 
covered wire. If the wiring is concealed as in the parti¬ 
tion of a new house, it is excellent practice to allow 
three or four inches of extra wire where the wires con¬ 
nect into the buttons. This allows access to the connec¬ 
tions from the front in case trouble develops in the system 
after the house is finished. 

It is very important that the ground connection be 
properly made; otherwise there is a constant source of 
trouble. 









































BELLS, ANNUNCIATORS, GAS LIGHTING 47 

Instructions for Making a Good Ground. —i. Scrape 
the pipe clean of scale and rust with a file or sand¬ 
paper. 



2 . Wrap from six to ten turns of the bare wire around 
the pipe and tie it tightly. 

3. Solder the wrapping to the pipe or wrap the wires 
and pipe with tin foil—the latter is preferable. 

4. Wrap the joint with friction tape. 
































































48 


PRACTICAL ELECTRIC WIRING 


The copper ground clamps used in grounding con- 
duit systems make excellent grounds for gas lighting 
systems, but are seldom employed because of the extra 
expense involved. 

Two plans are used for installing the wiring for a gas 
lighting system. One plan is to place the battery and 
spark coil in the basement or in some other inconspicu¬ 
ous place and connect the ground wire to the nearest 
gas pipe. Then it is only necessary to run one wire up 
through the house for the button plates or pendant 
burners. 

The other plan is to carry the ground wire through the 
house and ground it to each fixture that is wired. 

The latter plan, though more expensive, makes a more 
reliable installation. Gas pipe is considered a poor con¬ 
ductor because the lead used in the joints is sometimes 
of sufficient thickness to interrupt the circuit. 

The wires that run to the pendant and automatic gas 
burner often become grounded to the pipe and run down 
the battery. To prevent this a device called a battery 
cut-out is placed in series with the battery and spark coil, 
as shown in Fig. 32. One type is wired to close the 
circuit on an electric bell and battery after the current has 
passed for a period of time longer than that necessary 
to light the gas. Another type opens the circuit after 
current has passed for a few seconds. Battery cut-outs, 
though not absolutely necessary, often more than pay for 
themselves by minimizing battery expense. 

Wiring Fixtures.—In wiring a fixture for electric 
gas lighting, the wire or wires are usually concealed be- * 
tween the casing and gas pipe to the ball where the arms 
branch. The wires are then carried out through small 
drill holes in the casing and wrapped spirally around the 
arms out to the burners. 'Where the wires are exposed 
they may be painted to make them less conspicuous but a 
metallic paint should not be used unless the wires are 
rubber insulated. 


I 


BELLS, ANNUNCIATORS, GAS LIGHTING 49 

Multiple Gas Lighting. —In large rooms where a 
number of different gas burners are to be lighted simul¬ 
taneously, usually an induction coil and battery or a fric¬ 
tional machine is employed. A special burner, which has 
a short gap over the burner tip and contacts well insulated 
from the pipe, is used for this purpose. The burners are 
connected in series as shown in Fig. 33. Both contacts 
of all burners are insulated from the pipe except one 



Figure 33. 


contact on the last burner which is grounded to the pipe 
for the return circuit. 

A very small copper wire, about No. 24 or 26, is strung 
from burner to burner. The wire should be kept at 
least an inch and a half from the gas pipe and, where 
insulators are required, a glass tube should be used. For 
lighting a number of burners a multiple circuit switch 
may be required, so that the lighting may be done by 
sections. 

' Locating Trouble on Battery Systems. —If the bells 


































































50 


PRACTICAL ELECTRIC WIRING 


\ 


do not ring, the most likely cause is a dead battery. To 
test out the battery connect an ordinary bell across the 
terminals of each cell. If any of the cells do not ring 
the bell, they should be discarded for new ones. If the 
battery is in good order, look for an open circuit in the 
buttons. Next, look for a short circuit in the bell or bells 
and test each one separately. Next, the trouble may be 
due to a short circuit between the wires. As a last 
resort look for an open Circuit in the wiring. Where an 
open circuit is suspected at a point in the wiring, a length 
of good wire may be connected on each side of the sup¬ 
posed opening. 

If the bells ring continually, the trouble is probably 
due to the buttons making contact, or a short circuit of 
the wires leading to the button. 

Sources of Power for Low Voltage Systems. —A bat¬ 
tery of primary cells is usually employed for low voltage 
work. For open-circuit work, that is, where the cur¬ 
rent is used only at short intervals, as for bells, annun¬ 
ciators, etc., the Leclanche is commonly used. 

Leclanche Cells .—The Leclanche cell is made in two 
types ; namely, the wet and the dry cell. The wet cell con¬ 
sists of a glass jar container, a cylindrical carbon and a 
pencil zinc as elements, and a solution of sal ammoniac. 
The dry cell employs the same elements and solution, the 
difference being that the solution is in a paste instead of a 
liquid form. 

The wet cell is usually preferred in stationary work, 
as the upkeep is less than it is with dry cells. Under 
ordinary service these cells should last for a year, after 
which they may be renewed very easily. If the loss in 
voltage is due to evaporation of the solution, water may 
be added to bring the solution up to the usual level. The 
zinc should be examined at the same time, and if covered 
with a deposit, the latter should be scraped off. If the 
zinc has been almost wholly consumed, of course a new 
zinc should be used. 


i 


BELLS, ANNUNCIATORS, GAS LIGHTING 51 


The carbon element lasts much longer than the zinc, 
though after four or five zincs have been consumed the 
carbon should be renewed. The life of an old carbon 
may sometimes be renewed for a time by placing it in 
boiling water for twenty or thirty minutes. 

Renezving Cells .—To renew the solution place four 
ounces of sal ammoniac in the jar and add water until 
the jar is about three-fourths full. 

Dry cells are sometimes used for ringing bells, annun- 



Figure 34. Leclanche Wet Cell. 

fiators, etc. Two types of cells are manufactured, those 
built for automobile ignition and those for lighter work. 
The cells may be bought in either of the two types, 
the igniter for automobile use and the regular for light 
open-circuit use. The cells used should be fresh and 
it is not wise to purchase more than needed, as they 
deteriorate even though not in use. To test a cell con¬ 
nect an ammeter directly across the terminals. This 
connection should be closed only momentarily, as the 
short circuit thus formed will ruin the cell in a few 
minutes. A new cell should show at least 20 amperes 
of current on a short circuit and when it is discharged 
below five it should be discarded. 

Gravity Cells .—For closed circuit work the gravity cell 
or one of the several other cells adapted to this class of 
work should be used. The gravity cell derives its name 




















52 


PRACTICAL ELECTRIC WIRING 


from the way in which its two fluids are separated, that 
is, by gravity. As, illustrated by Fig. 35 there is a crow¬ 
foot of zinc near the top of the cell and a similar form 
of copper in the bottom. The solution before use is 
copper sulphate, but the chemical action of the copper 
sulphate upon the zinc causes zinc sulphate to be formed 
as the lighter liquid. 

Charging Cells .—To charge a gravity cell place one 
pound of copper sulphate crystals in the jar and add 
water to bring the solution to the proper level. Dissolve 
the copper sulphate until the solution is saturated and 
leave the cell on short circuit overnight. Should the cell 



Figure 35. Gravity Cells. 


be needed for immediate use a little sulphuric acid added 
to the solution will facilitate the action. This solution 
when working will have what is known as the blue line, 
that is, the line where the blue and white liquids meet. 
This line should be kept midway between the top and the 
bottom of the cell. If the blue line is too low the cell 
has been worked too hard and should be left on open 
circuit, but if the blue line is too high the cell has not been 
worked enough and should be put to work. 

Bell-ringing Transformers .—Bells and other low volt¬ 
age devices are sometimes operated by bell-ringing trans¬ 
formers. Such a transformer has four wires passing 
out from it, two of which are to be connected across the 
electric light wires and two others which are to be con¬ 
nected to the bell wires in place of the battery. The 
electric light wires to which the transformer is con- 


1 
































BELLS, ANNUNCIATORS, GAS LIGHTING 53 


nected must of course supply an alternating current. The 
connections should be made as shown in Fig. 36A. If 
one transformer is not strong enough to operate the 
bells, two may be used by connecting them as shown in 
Fig. 36B. If the transformers thus connected do not fur¬ 




nish any current the connections of one transformer on 
the bell side must be reversed. 

Motor Generator Sets .—Motor generator sets as shown 
in Fig. 37 may be used for ringing bells on a large scale 
or for other low voltage work. The motor for the set 
is wound for no or 220 volts of alternating current and 
the generator furnishes 15 volts of direct current, which 


























54 


PRACTICAL ELECTRIC WIRING 


may be reduced by means of a field rheostat to suit the 
resistance of the circuit. As the current drawn from 
the generator is likely to be rather large, wires leading 


Figure 37. Motor Generator Set. 

from it to the bells should be heavier than bell wires. It 
is good practice to use No. 14 or No. 12 for the main 
wires leading out from the generator and tap off with 
No. 18 bell wire for branch wires to different sets of 
bells. 

' QUESTIONS. 

1. What are the code requirements for wiring for bells or 

other low voltage wiring? 

2. Explain the principle of operation of a vibrating bell. 

3. Describe two methods of carrying bell wires concealed. 

4. How should wires be secured under binding screws? 

5. How are coils made in bell wires? Where are they 

used? Why are they used? 

6. What space should be allowed between staples on bell 

wires? 

7. Are joints in bell wiring usually soldered and taped? 

8. In open work, may the wires be run near each other? 

Why are staples “staggered” ? 

9. How may the kinks be taken out of bell wire? 

10. Describe a method of crossing one wire over another 
in open bell wiring. 




I 


BELLS, ANNUNCIATORS, GAS LIGHTING 55 


11. How may open bell wiring be made less noticeable? 

12. Do bells operate better when connected in series or in 

multiple? 

13. Explain a method of operating bells in series. 

14. How may a wire in a low voltage system sometimes 

be eliminated? 

15. Why is an automatic drop used with a burglar alarm 

system ? 

16. Explain the operation of a closed circuit burglar alarm 

system. 

17. How many wires are required in wiring for a simple 

annunciator? 

18. Explain the operation of the gravity drop annuncia¬ 

tor. 

19. Explain the operation of the needle type annunciator. 

20. In wiring for needle drop annunciators, is it sometimes 

necessary to reverse the polarity of the battery? 
Explain. 

21. How many wires are required in wiring for a return 

call annunciator? 

22. Explain the lighting of gas with a pendant gas burner. 

23. Explain the lighting and controlling of gas with an 

automatic gas burner. 

24. What is a spark coil, and what is its use? 

25. Explain the operation of a battery cut-out. 

26.. Explain in detail a method of grounding a wire to a 
gas pipe. 

27. Is a gas pipe considered a good conductor for the return 

circuit to a burner? Explain another method of 
wiring for the return circuit. 

28. Give a plan of wiring a fixture for gas lighting. 

29. How are a number of gas burners lighted simultane¬ 

ously by electricity ? 

30. Explain in detail the different things to be done in 

locating trouble on a battery system. 

31. What is the construction of a Leclanche wet cell? 

32. How long should a Leclanche cell last, and how may 

it be renewed? 

33. How much current should a fresh dry cell furnish on 

short circuit? 


56 PRACTICAL ELECTRIC WIRING 

34. For what class of work is the gravity cell used? What 

is the construction? 

35. How may a gravity cell be charged? 

36. Explain the connecting of two bell-ringing transformers 

to work in series on a bell circuit. 


1 


Exercises for Practice. 



Re /ay 


$ 

l <s> 

—il'l— 

R,I 

— i|'h 

i H Q 


<J 8 


i—q—^ 


57 
















































































































































































































































CHAPTER IV 


OPEN WIRING 

Open wiring in a finished house may be done with 
either knobs or cleats, but two wire cleats are usually 
used because less time is required to install them. As is 
the arrangement for practically all other systems of wir¬ 
ing, the fittings for lamps and power are connected in 
multiple; that is, connected between the two wires of the 
circuit. 

Switches are cut in the line between the device to be 
controlled and the source of power. Single-pole switches 
break one side of the line and double-pole switches break 
both sides. 

Diagram.— The following wiring diagram for a 
small house will enable us to explain in detail the execu¬ 
tion of the work. 

To proceed as a wireman or contractor, after the num¬ 
ber of outlets and their location are decided upon, the 
next step is to make a list of material needed. 

Material Required .—The following is an approximate 
list of material for wiring a house according to the fol¬ 
lowing diagram: 

i main-line entrance switch and cut-out, two wire, 30 
amperes capacity 

1 double-branch block two wire to two wire 

8 cleat receptacles 

3 cleat rosettes 

3 key sockets 
21 two-wire cleats 
28 size 4 \ split knobs 

2 tie knobs 


59 


Cutout O O Switch 



W Is 

^ Ok 



60 


































































































































OPEN WIRING 


61 


i single-pole snap switch 

1 double-pole snap switch 

2 sub-bases for switches 

i doz. if-inch No. 6 round-head blued wood screws 
20 3-inch porcelain tubes 
io 6-inch porcelain tubes 

300 feet of No. 14 single-braid rubber-covered wire 
1 stamped metal or cast-iron box 6x9x4 inches 
1 large box bushing 
6 box bushings for §-inch hole 
10 feet of |-inch circular loom 
1 4-inch wood canopy block 
I two-light fixture, brushed brass finish 

1 gross 2^-inch No. 8 wood screws, flat head, bright 
J gross 2-inch No. 8 wood screws, round head, blued 

2 doz. i^-inch No. 7 wood screws, flat head, bright 
1 pound of solder wire 

Tib. box of soldering paste 

1 i-lb. roll of friction tape 

2 15-ampere plug fuses 
4 6-ampere plug fuses 

10 feet No. 18 fixture wire 

Tools Required .—The following tools are needed to 
install the wiring: 

1 small screw driver, cabinet style 
1 large screw driver, machinist’s style 
1 ratchet bit brace 
1 f-inch bit 
1 pair 7-inch pliers 
1 15-ounce nail hammer 
1 gasoline or alcohol soldering torch 
1 jackknife 

Execution of the Work. —Entering with Mains .—In 
the execution of this job as planned, the wires for the 
mains should come into the building through porcelain 
tubes long enough to bush the entire length of the hole. 
The service entrance should be made well above the 


62 


PRACTICAL ELECTRIC WIRING 


second-story window and the wires carried on knobs or 
cleats to the cabinet box if it is located on the second 
floor. A better mechanical, and perhaps a more satis¬ 
factory method, is to locate the cabinet box either on 
the first floor or in the basement and run the mains from 
the point of entrance in rigid conduit to the box. It is 
always better to consult the insurance and city author¬ 
ities about running the entrance wires, as there are many 
local rules. 

Switch and Cabinet Boxes .—In the present installation 
we will suppose the wires are carried to the cabinet box 
on knobs, passed into the box through separate bushed 
holes and fastened to the binding screws in the cut-out. 
Two wires from the service switch and two from the 
central contacts on the double-branch block are carried 
through one large box bushing to be connected to the 
electric meter. Wires for the branch circuit pass out of 
the box bushings and are carried on cleats or knobs to 
the fittings to be installed. 

Branch Circuits .—On branch circuit No. i the first cleat 
should be within three inches of the box to take the 
strain off the wires and small binding screws where they 
are dead-ended in the branch block. The second cleat 
may be four and a half feet away from the first, and 
the cleat rosette, which is considered as a cleat so far 
as supporting the wires is concerned, may be placed any 
distance up to four and a half feet from other cleats. 

Tap Circuits .—Where there is a circuit tapped off 
from a line, the strain should be taken off the joint by 
placing cleats near the joints on all wires passing out, as 
shown by cleats 4, 5 and 7. Instructions for soldering 
and taping a joint are given in Chapter II. In case a 
blow-torch is used care must be taken to prevent smok¬ 
ing or burning the ceiling or wall. Place a piece of 
tin or asbestos about four inches square between the 
joint and the wall and proceed as with other soldering. 

The porcelain tube shown at the joint is threaded over 

i 


1 


OPEN WIRING 


63 


one wire to insulate it from the other live wire. There 
must be some method of holding the tube in place. In 
this case it is done by placing the cleat near enough on 
one side so that with the joint on the other it will pre¬ 
vent the tube’s slipping either way. Where the wires 
cross over other wires or pipes the tubes are generally 
held in place by two other methods, one of which is to 
tape the wires at both ends of the tube with sufficient 
layers of tape to keep it from slipping either way. The 
other method is to drive a wooden peg between the wire 
and the tube. 

Rosettes and Receptacles .—To install cleat rosettes and 
cleat receptacles in a line, the wires are scraped clean 
of the insulation for about one-half inch and the wires 
passed under the binding screws. Where wires are dead- 
ended at a rosette, receptacle or other fitting, they should 
be scraped clean of the insulation and passed around the 
binding screw to the right, so that tightening the screw 
will tend to draw the wire toward the center of the 
screw. 

In making a double tee joint as shown between cleats 
Nos. 8 and 9, there are several styles of joints used but 
the one shown in Fig. 39 makes the neatest and best 
joint mechanically. 

Scrape the wire already installed for about one and a 
half inches, remove the insulation from the ends of the 
other wires, and wind them tightly each way round the 
wire installed. 

A “dead end” is seldom made on cleats, but where one 
is used the wire should be passed back over the cleat and 
wrapped round the wire for three or four turns, as shown 
at cleat No. 10. To get the wrappings closer together 
and to tighten the wires, grip the turns with a pair of 
pliers and pull them round in the original direction as 
far as possible. 

Wiring between Rooms .—In going from one room to 
another through a partition, holes should be bored and 


6 4 


PRACTICAL ELECTRIC WIRING 


porcelain tubes inserted long enough to bush the holes 
through the entire partition, as shown in the foregoing 
wiring plan. 

In making a right-angle turn, the cleats should be 
placed near each other and at right angles, as shown by 
Nos. 12 and 13. The inside wire makes almost a right 
angle while the outside wire makes a gradual curve from 
one cleat to another. 

Mounting Switches .—In mounting single-pole and dou¬ 



ble-pole snap switches the usual practice is to place them 
four feet two inches from the floor; however, they may 
be mounted higher or lower to suit the convenience of 
the customer. Snap switches must have sub-bases of 
porcelain or similar material placed between the switch 
and the wall. Two screws only are required to hold both 
the switch and the sub-base, screws being used that are 
long enough to pass through both and secure them firmly. 

Wires may be run open on side walls where they are 
not subjected to mechanical injury. Where the wires are 
apt to be disturbed they should be incased in rigid con¬ 
duit, wood or metal molding on the side walls. 

Fixtures .—Fixtures are usually ordered not wired and 


1 

















OPEN WIRING 


65 


are wired in the shop or on the job. To wire the fix¬ 
ture shown in the following diagram it is necessary to 
fish two wires from the canopy of the fixture down into 
the ball at the bottom. There should be at least six 
inches of free wire left in the canopy to tap to the branch 
wires. Wires are connected to the binding screws in the 



Figure 40. 


sockets and fished through the fixture-arms to the ball. 
The wires in this ball are connected in multiple, as shown 
in the diagram, and are usually joined with a rat-tail 
joint, which is described in Chapter II. 

These joints must be soldered, of course, and taped 
with rubber and friction tape. 

To hang a fixture on a plastered ceiling a wooden can¬ 
opy block should be installed for the purpose of support¬ 
ing the fixture. Before this block is installed two f-inch 
holes should be drilled from the outside of the block to 
the center to carry the wires into the center of the can- 














66 


PRACTICAL ELECTRIC WIRING 


opy. The holes should be about 2\ inches apart and 
drilled at an angle so that they will come out under the 
canopy. (See Figs. 40 and 41.) 

The fixture is secured to the block by screws which 
are passed through the holes in the crowfoot, from which 
the fixture is hung. The joint to be used in the canopy 
is the fixture joint described in Chapter II. 

Time-saving Methods .—In installing cleat work much 
time will be saved and a neater job will be made if the 
wires are drawn taut between distant cleats. That is, 
referring again to the preceding house wiring diagram, 



Figure 41. 

beginning from the cabinet box put up cleat No. 1 with 
the wires in place and tighten up the screws, then instead 
of installing cleat No. 2 install cleat No. 4, which is about 
sixteen feet away, then place the wires in the grooves in 
the cleat, draw the wires taut and tighten up on the 
screws. After the wires have been drawn taut in this 
way it is an easy matter to put in the other intermediate 
cleats and rosettes and get a straight line of wiring. 

One of the best methods of drawing the wires taut is 
the following: Having the wires secured in one cleat, 
carry them forward to the other, put up the cleat with 
the wires in place and turn the screws until the wire will 
barely slide through the grooves. After having tightened 
the wires with the hands as much as possible, grip one 




OPEN WIRING 


67 


wire to be tightened with a pair of pliers close to the 
cleat and turn them in toward the bottom of the cleat and 
at the same time with a screw driver tighten the screw 
nearest this wire. If the pliers injure the insulation of 
the wire a piece of sheet fiber may be placed over the 
wire. 

Drop Cords .—In open work drop cords are generally 
used and therefore should be made strong mechanically. 
The “drop,'' as it is usually called, consists of three parts: 
rosette, cord, ^nd socket. The rosette should have no ex¬ 
posed metal contacts; the cord should be No. 18 twisted 
lamp cord, or reinforced cord; the socket should be of 
some approved make and should be suspended at least 
six feet from the floor. In damp places “packing house 
cord” should be used. Metal sockets may be used in dry 
places, but porcelain or other weatherproof sockets should 
certainly be used in damp places. Usual practice in wir¬ 
ing a residence is to install metal sockets in all rooms 
except the bathroom which, with the basement and damp 
porches, has weatherproof sockets. 

The National Electric Code requires that some 
method be employed to take the strain off the small wires 
and binding screws at the rosette and socket. To accom¬ 
plish this the cord, should have a knot tied in it that is 
as bulky as possible, and this knot should then be taped 
with friction tape until it will not readily pass through 
the hole. The underwriter knot which is shown on page 
68 is considered the best knot for this purpose. 

To fasten the stranded wires of the lamp cord under 
the binding screws in the rosette or socket all the separate 
wires of the strand should be twisted together and then 
passed round the screw. This not only increases the con¬ 
ductivity of the connection but also prevents stray wires 
of the strand from touching the other side of the circuit 
and thereby causing a short circuit. 

Running cleat work or knob work on the lower side of 
the joists, where the wires are exposed to mechanical 



Figure 42. The Underwriter Knot. 

68 







OPEN WIRING 


69 


injury, may be done in either of two ways. One is to 
carry the wires and insulators on a wooden board \ inch 
thick and 3 inches wide. The other is to fasten the in¬ 
sulators directly upon the underneath side of the joists 
and run guard strips $ inch in thickness and as high as 
the insulators on each side, and close to the wires. 

Branch circuit No. 2 of the foregoing wiring diagram 
shows a circuit run on porcelain split knobs. Where the 
voltage is no volts and there is an even number of wires 
there is no particular advantage in using knobs for open 
work, although they are sometimes used, especially for 
motors, and should be mentioned. There are two types 
of knobs; namely, the split knob and the solid knob. 
Split knobs are now approved by the Code and are 
used almost entirely in preference to the solid or tie knob. 
The tie knob is sometimes used in connection wit 1 ; the 
split knobs but only as a “dead end” knob. In making 
a turn with a split knob as a support, the wire should 
be placed in the groove on the outside of the screw, so 
that the screw will prevent the wire’s slipping out of the 
groove should it become loose. 

Either tie knobs or split knobs may be used on a dead 
end, the same method of dead-ending the wires being 
used for both. Pass the wire round the knob and back 
over itself four or five times as in dead-ending at a 
cleat. 

Tests .—Tests of open work are seldom made before 
the power is turned on; however, when the contractor 
wants to be sure of the wiring before he leaves it, he 
should make a test for short and open circuits. The 
most common method of making these tests is with a 
magneto, though a bell and battery may also be used. 
When using a magneto connect the wires from the mag¬ 
neto to the wires of one circuit of the system. This is 
usually done by passing the wires from the magneto 
under the binding screws at the cut-out with the wires of 
the circuit. With the connections thus made, turn the 


70 


PRACTICAL ELECTRIC WIRING 


c 

crank of the magneto and if the bells ring with no lamps 
in the sockets, there is a short circuit on the system. If 
there is no ring the wiring is free from short circuits. 
If a short circuit is indicated, it will probably be found 
in a rosette, socket, or fixture. 

The other test to be made is for open circuits. Leaving 
the magneto connected in the same way as for the first 
test, screw a lamp into a socket, turn on the key or 
switch and turn the crank of the magneto. If the bells 
ring the circuit is complete, but if the bells do not ring 
look for an open circuit between this socket and the 
magneto. This test should be performed in a similar way 
upon every lamp socket in the system. A vibrating bell 
and a battery may be used to perform the above tests; 
but when testing for open circuits a fuse plug should 
be screwed into the socket or a screw driver should be 
helu across the contacts in the socket, because a lamp 
has too high a resistance to transmit the battery current. 

Wood Molding. —Installing wires in wood mold¬ 
ing is often done in connection with other systems, 
but a wiring job alone is seldom made in wooden mold¬ 
ing. Wooden molding cannot be used in damp places; 
therefore damp rooms, cellars and outside spaces must 
be wired in some other manner. 

Where the installation is to be entirely in wooden 
molding the cabinet box should be located on the first or 
second floor. The mains should be passed through the 
outside walls in porcelain tubes long enough to bush the 
entire length of the holes. The wires can then be carried 
in wooden molding down to the cabinet box and from 
the cabinet box, the branch-circuit wires can be passed 
out in molding to the different floors. 

The molding used must be covered or painted with 
at least two coats of waterproof material or be impreg¬ 
nated with a moisture repellant. 

Parts .—The molding consists of two parts; namely, a 
backing and a capping. The backing is secured to the 


i 


OPEN WIRING 


7 1 


surface wired over; the wires are then inserted in the 
grooves and the capping is tacked on with small nails 
called capping brads. This holds the wires in place and 
presents a finished appearance. 

Where wood molding is laid on plaster it should be se¬ 
cured with wood screws. It makes a better job me¬ 
chanically to use them for securing the backing through¬ 
out the installation. However, sometimes nails are used 
instead on wooden surfaces. To install molding with 
screws, holes should be drilled in the backing for the 
screws to pass through, and these holes should be counter¬ 
sunk, so that the screw heads will go in flush with the 
surface. 

In a building where the molding is to be run on an 
outside brick wall that may be damp, a backing of at least 
J-inch thickness should be placed behind the molding. 
Usual practice is to place a piece of the molding backing 
under the molding, with the groove side toward the wall. 

Support .—To fasten wood backing to a brick wall the 
usual method is to drill a hole three or four inches deep 
with a star drill or cold chisel and to drive into this hole 
a wooden plug which is then sawed off close to the wall. 
To this plug the wooden backing is secured by a screw. 

In a building of hollow tile construction toggle bolts 
make the best support for the molding. A hole is drilled 
into the tile large enough for the bolt with the toggle 
arrangement to be inserted. Then the toggle turns, mak¬ 
ing a tee that will not pull through the hole, and the bolt 
is tightened. 

Wooden molding is not approved for any concealed 
places. Therefore in passing through floors and parti¬ 
tions some more secure form of insulation is required. 
In passing through a partition the molding is carried to 
the partition on both sides and the wires are passed 
through the wall in porcelain tubes long enough to bush 
the entire length of the hole. In passing through floors 
the same method is used with the addition of a “kicking 


72 


PRACTICAL ELECTRIC WIRING 


box” to protect the wires and tubes where they pass down 
through the floor. There are two types of kicking boxes, 
one of cast-iron and one constructed of wood, as shown 
in Figs. 44 and 43. 

The cast-iron kicking box shown in Fig. 44 may be 
bought for any size of molding and makes a very neat 
appearance. The wooden box, as shown in Fig. 43, may 
be built by the wireman and answers very well as a sub¬ 
stitute for the metal box. 



Where a right-angle turn is made with wooden molding 
both the backing and the capping should be mitered to 
make a neat joint, as shown in Fig. 45. Some time will 
be saved and perhaps neater work will result if the cap¬ 
ping and backing are held together and the miters cut in 
both at the same time. 

Mitering .—For mitering wooden molding, wooden 
miter boxes, iron miter frames, or combination squares 
may be used. The combination square is more popular 
for jobs outside the shop because it is lighter and less 
awkward to carry than either of the other two. 

Where a single-pole switch is to be inserted in one of 
the wires that pass in a line of molding, the wires are 
usually carried to the switch in an additional piece of 
molding which is butted against the line already installed. 


1 























OPEN WIRING 


73 


The usual method is to cut grooves in the side of the 
main line of the molding through which the wires are 
passed down into the molding leading to the switch, as 
shown in Fig. 46. Fig. 47 shows a much neater method 
of cutting in for a switch. In this plan an A-shaped 
block is cut out of the main line of molding, and the end 




of the switch molding is cut A-shaped to fit the slot. 
With this method the grooves of the two moldings fit 
together, which fact avoids the necessity of cutting 
grooves for the wires to pass out of the main run of 
molding. 

No joints or splices are permitted in the wires in the 
molding; that is, the wires must run in continuous lengths 
from outlet to outlet or from fitting to fitting. Where 
tap circuits are taken from a line of molding for one or 
more lights, a porcelain fitting called a taplet is used to 
take the place of joints. The taplet, as shown in Fig. 
48, consists of two parts, a base and a cover. 
























74 


PRACTICAL ELECTRIC WIRING 


The base is first secured to the backing and the wires 
that pass through are bared of the insulation for a short 
distance and are passed under the binding screws, as 
shown in Fig. 48. For the tap circuit the end wires are 
secured under the other set of binding screws and -are 
passed out to the lights or other current-consuming de¬ 
vices. The porcelain cover is then placed over the base 
to conceal the live metal contacts. The reader must not 



Figure 48. 


mistake the use of this taplet and use it to tap off for a 
single-pole switch because such an arrangement, when 
the switch is closed, will make a short circuit on the 
line. The taplet is only used when it is desired to put two 
sets of current-consuming devices in multiple. 

Where rigid conduit is used in connection with wood 
molding there are three approved methods of passing 
the wires from molding to conduit. The first is to use 
a condulet, as shown in Fig. 49; the second is to use a 
condulet made for this purpose, as shown in Fig. 51; and 
the third is to carry the wires into a junction box through 
porcelain tubes or box bushings, as shown in Fig. 50. 

Switches .—Snap switches are used almost entirely on 
a wooden molding installation, because they are less ex- 











OPEN WIRING 


75 


pensive than others and make a neater appearance. The 
switch should have the regulation porcelain sub-base in¬ 
stalled under it to insulate it from the surface wired 
over. The appearance of the job may be improved if 
the wireman will let the capping extend over the sub¬ 
base and cut the end circular in form to fit up round the 
switch, as shown in Fig. 52. This covers the wires where 



Figure 49. 


they pass into the switch and helps to add neatness to 
molding work. 

To install a fixture in connection with wooden molding, 
a wooden canopy block should be used similar to the one 
previously described in this chapter. One-fourth inch 
holes should be drilled from the outside to the center 
of the block, as shown in Fig. 53, through which the 
wires are carried. 

This method avoids the necessity of cutting the canopy 



where the wires pass into it and gives a much neater 
finish to the job. The fixture is hung with a crowfoot 
as described for straight electric fixtures in Chapter V. 

Molding receptacles and molding rosettes are of two 
kinds; those that sit on the top of the backing and those 
that lie on the surface and have the molding butted 
against them. The former type is usually employed be- 













7 6 


PRACTICAL ELECTRIC WIRING 


cause it does not necessitate cutting of the backing where 
the fitting is to be installed. 

Wooden molding may often be made less conspicuous 
by painting it the same color as the surface over which 



Figure 51. 


the molding is placed. This is especially desirable if 
there is a contrast in colors between the molding and the 
surface. 

Wooden molding is often used with open work wiring, 
where the wires pass down on the side walls for switches 
or pass through the floors. Besides making a neater 



job it provides an excellent device for protecting the 
wires from mechanical injury. 

Wooden molding of a decorative character is some¬ 
times used in rooms that are adapted for it. The most 
common decorative method is to make it represent a 
picture molding. In this case it is installed all round the 
room, and the wires are run in it along the walls to the 




OPEN WIRING 


77 


different outlets. The fittings for lights and fixtures are 
seldom installed on the molding itself, the usual position 

UEsD 



Figure 53. 


for outlets being either below on the wall or above on the 
ceiling. The wires for the outlets are carried through 



Figure 54. 























78 


PRACTICAL ELECTRIC WIRING 


the backing and are fished through the wall in circular 
loom to the outlets, as shown in Fig. 54. 

The final tests on the installation should be for short 
circuits and open circuits, as previously described in this 
chapter. 

QUESTIONS. 

A. OPEN WORK. 

1. How are current-consuming devices usually connected 

on a wiring circuit? 

2. How are switches connected to control current-consum¬ 

ing devices? 

3. What is the difference between single-pole and double¬ 

pole switches? 

4. What tools are necessary for an installation of open 

work wiring? 

5. Describe two plans for carrying the main wires into 

the building for open work. 

6. What is the greatest distance allowed between cleats 

or knobs in open work wiring? 

7. How is a tap circuit made from a line of cleat wiring? 

8. When soldering wires in open work with a torch, how 

may the surface behind the joint be protected from 
the flame of the torch? 

9. Describe two approved methods of holding tubes in 

place when placed over wires. 

10. How is a “dead end” made in cleat work? 

«* 

11. How should wires be insulated where they pass through 

partitions? 

12. How is a right-angle turn made in wiring with cleats? 

13. In mounting single-pole snap switches, what is the 

usual height above the floor? How should they be 
insulated from the wall ? 

14. When and how should wires be protected on side walls? 

15. Explain the method of wiring a two-light electric 

fixture. 

16. Explain in detail the method of installing a fixture for 

open work on a plastered ceiling. 


OPEN WIRING 


79 


17. Explain in detail a time-saving method for installing 

cleat work. 

18. How may the wires be drawn taut in the cleats? 

19. How must lamp cord be supported where it passes into 

the rosette and socket? 

20. Show the method of tying the underwriter’s knot. 

21. What type of knob is commonly used for knob wiring? 

22. Explain the method of making turns with split knobs. 

23. How is a “dead end” made on knobs? 

24. Explain two methods of installing knob or cleat wiring 

on the underneath side of joists. 

25. Explain the method of testing with a magneto for short 

circuits on a wiring system. 

26. Explain the method of testing with a magneto for open 

circuits. 

B. WOODEN MOLDING. 

1. Explain a method of making a service entrance for a 

building with wooden molding. 

2. Explain the method of installing wooden molding. 

3. How should molding be protected from the moisture of 

a brick wall ? 

4. How may w.ooden molding be supported on (a) Brick 

walls? (b) Hollow tile construction? 

5. How is wooden molding wiring carried through (a) 

Partitions? (b) Floors? 

6. How should turns be made with wooden molding? 

7. Explain the plan for carrying wires from a line of 

molding to a single-pole snap switch. 

8. How is a tap circuit made from a line of wooden 

molding? 

9. Explain three methods of passing wires from wooden 

molding to conduit. 

10. Explain a method of installing an electric fixture on a 

molding circuit. 

11. How may wooden molding often be made less con¬ 

spicuous ? 

12. Explain the use of decorative wooden molding. 


Exercises for Practice. 



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84 


I 













































































































































CHAPTER V 


CONCEALED KNOB AND TUBE WIRING 

I. New House.—In concealed knob and tube work 
in a new house part of the work must be done at two 
stages in the process of building. The running of the 
circuits, or the “roughing-in job,” as it is usually called, 
must be done when the floor joists are accessible. The 
ideal time to do this is when the floor joists are laid and 
the studding for all the rooms is installed. The remain¬ 
ing work on the job, namely, the installation of switches, 
‘'cut-outs” and other fittings that may come in the con¬ 
tract, should be done after the house is finished, that is, 
after the floors are laid and the plastering is completed. 

Planning Installation .—To enable the electrical con¬ 
tractor properly to lay out the installation, he should be 
furnished with a blue print of the plans of the building, 
on which are shown by symbols the location of outlets 
for lights and switches, the number of fifty-watt lamps 
for each lamp outlet, and the number and kind of switches 
for the switch outlets. From the plans the next step is 
to locate the entrance switch, the entrance cut-out and 
cabinet box, and trace out the branch circuits. This must 
be done according to the rules applied to other systems. 
The wiring on branch circuits should now be arranged 
so that not more than twelve lights will be on any one 
circuit. 

In doing coficealed knob and tube work, the code re¬ 
quirements should be kept constantly in mind. One of 
the most important of these is the rule that wires must 
be kept at least five inches apart when run on the insu¬ 
lators. 


85 





86 

















































CONCEALED KNOB AND TUBE WIRING 87 


Entering the Building .—For bringing mains into the 
house, the arrangement shown in Fig. 55 is considered 
superior to all others, from a mechanical as well as an 
electrical standpoint. 

The mains are carried in rigid conduit from the point 
of entrance on the second floor down through the side 
walls to the iron box in the cellar. In this box are 
placed the main-line switch and cut-out, and branch 
blocks. Wires for meter and branch circuits are carried 
out through porcelain box bushings. 

Branch Circuits .—All concealed wires for the branch 
circuits are usually carried on split knobs or are passed 
through porcelain tubes to lights or other current-con¬ 
suming appliances. If conditions make it desirable, wires 
may be run in rigid conduit or in circular loom. 

Where curves are made with knob wiring, the knob 
should be placed so that the screw comes on the inside 
of the curve to prevent the wire’s slipping out of its 
groove, as shown in Fig. 55. Where wires are 
passed through floor beams or joists in porcelain tubes, 
the tubes should be long enough to bush the entire length 
of the hole and the holes should be bored at a slight 
angle from the horizontal, so that when the tube is in¬ 
serted with the head up, gravity will prevent its slipping 
out of the hole. 

Boring Floor Joists .—111 boring the holes in the floor 
joists for the tubes and wires, some wire and much time 
will be saved if the electrician will use a bit with a long 
shank instead of the ordinary carpenter’s bit. As is 
shown in Fig. 56, the long bit permits the swing of the 
brace to come between the first and the second joists from 
the one being bored, which fact allows the hole to be 
bored more nearly at right angles to the joist, making the 
hole shorter. 

A f-inch bit is required for boring holes for tubes of 
J-inch internal diameter. The writer recommends a bit 
called the “ship’s auger.” However, if this cannot readily 


88 


PRACTICAL ELECTRIC WIRING 


be secured, it is a fairly easy matter for a blacksmith to 
weld an extension to a carpenter’s bit, which will answer 
the purpose. 

Much energy is often wasted in boring joists, because 
the wireman takes a position that is a strain on him and 
does not increase the rapidity of boring. If a good bit 
is used, it is not necessary for the wireman to get behind 
the brace and push with all his might to make it feed. 
A better position is to stand or sit beside the brace, give 
the butt of the brace a tap with the palm of the hand to 



start the bit and turn the brace at the same time, bearing 
on the brace with one hand to make it feed. 

Inserting Wires .—In threading the wires into the holes 
that have been bored in the joists for the tubes, the 
wireman will find it much easier to thread the wires 
through the tubes and leave the tubes between the joists 
while the wires are being pulled in, as shown in Fig. 57. 

This allows the wire to be pulled more nearly straight 
through the holes and permits longer pulls than other¬ 
wise could be made. After the wires have been pulled 
through in this way for the entire length of the run across 
the joists, the 'tubes may then be inserted in the holes, 
as shown in Fig. 58. 

Tubes should always be placed in the hole with the 
head up, except where there is to be a right-angle turn 





CONCEALED KNOB AND TUBE WIRING 89 


at the lower point of the hole. In this case the head of 
the tube should be placed down, so that the pull on the 
curve of the wire, which is stronger than the gravity of 
the tube, will hold it in place. 

Where wires pass up from one floor to another in a 
partition that is to be plastered, besides passing through 
a tube that bushes the entire length of the hole in the 
floor beam, there should be an additional 4-inch tube 
placed on the wire above the hole to protect it from any 
plaster which may fall and accumulate round it. 

Split knobs are held in place by two methods, that is, 
with wood screws or nails, and leather heads. Nails and 



[Figure 57. Figure 58. Figure 59. 


leather heads are being used almost entirely now for se¬ 
curing the knobs in concealed knob and tube work, be¬ 
cause with them much less time is required to do the 
wiring. The nail used is the ordinary wire head nail, 
which must be long enough to pass through the knob 
and into the wood for a distance equal to half the height 
of the knob. For a No. Si split knob, which carries a 
No. 14 wire, a 10-penny wire head nail should be used. 
The leather washer is designed to act as a cushion be¬ 
tween the head of the nail and the knob. 

Wires Parallel to Joists .—Where wires are run on and 

\ 

parallel to studding, joists or rafters, the wires should 
be run on separate timbers or on opposite sides of the 
same timber. Sometimes the timbers are wide enough to 
allow the 5-inch spacing between the wires on the same 
side of the timber, but this is not considered good prac¬ 
tice and wires run over each other on the same timber 
will not be approved by the electrical inspector. 














90 


PRACTICAL ELECTRIC WIRING 


Fixture Outlets .—To make a fixture or drop cord outlet 
in concealed knob and tube work, a board or i inch thick 
and 6 inches wide is nailed between the joists with its un¬ 
der side just back of the under side of the joists, as shown 
in Fig. 60. Two ^-inch holes are drilled into the board 
about half an inch apart, through which the wires and 
the circular loom are to be passed. The wires should be 
supported by knobs near the outlet and encased in cir¬ 
cular loom through the outlet. The loom should extend 
from the knobs, through the outlet holes, and 2^4 
inches below the board. The wires should extend about 
6 inches below the outlet to allow for tapping with the 
fixture wire. 

The board in the outlet described serves as a support 
to the canopy block, which in turn supports the fixture. 
Screws of sufficient length to pass through the canopy 
block, plaster and into the board should be used. The 
method just described is for “straight electric" fixtures, 
that is, where there is to be no gas piping connected 
with the fixtures. Where the fixture is to be both gas 
and electric, known as a “combination,” the board is 
unnecessary, the fixture being supported by the gas pipe, 
as shown in Fig. 6i. 

In work where there is to be both gas and electricity, 
the gas fitter should have the house piped for gas before 
the electrician comes upon the job. In this case the 
outlets have been located by the gas fitter and it is only 
necessary for the wireman to bore the holes beside the 
gas pipe outlet and pass the wires and circular loom 
through the holes. Where there is no board near the 
ceiling on which to support the wires and loom, they 
may be held to the gas pipe by friction tape passed round 
them, as shown in Fig. 6i. 

The wires for straight electric combination fixtures 
and drop cord outlets are twisted together and left till the 
building is completed, when the fixtures are hung and the 
rosettes and switches installed. 


CONCEALED KNOB AND TUBE WIRING 


91 


Flush Switches .—In concealed work flush switches of 
the push button type are used almost entirely, because 
they make a much neater appearance. These switches 



must be mounted in iron switch boxes, of which there are 
two types; namely, the one for circular loom and the one 
for conduit. The box used in concealed knob and tube 
work has punchings cut for circular loom. Where the 



height of the box is not specified by the customer, usual 
practice is to place the center of the box four feet two 
inches above the floor. 

To install a flush switch, the box should be held in 
proper position between two cleats long enough to reach 


























92 


PRACTICAL ELECTRIC WIRING 


between adjacent studding. Then nail the cleats to the 
studding, flush with the front side of the same, one 
against the top and one against the under side of the 
box. Next hold the box in the hand and with the edge 
of the hammer face knock out as many plugs as there are 
wires to enter the box. Then fasten the box to the cleats 
previously installed, with wood screws. Where the wall 
is to be plastered, a flush switch box should be installed, 
so that the front of the box lies one-half inch from the 
front surface of the studding, which with the usual depth 
of plaster makes the box accessible after the house is 
completed and also assures the wireman that the box will 
not extend out from the plaster. By means of movable 
ears on the front of the box, its distance from the front of 
the studding may be adjusted. This is done by loosening 
the screws by which the ears are fastened and turning 
the ears around. The wires passing into the box should 
be encased in circular loom from the knobs through the 
holes into the box, as shown in Fig. 62. There is gen¬ 
erally some device provided in the box for clamping the 
circular loom to prevent its slipping out of the holes. 

Where more than one switch is to be installed at a 
switch outlet, a switch box called a gang switch box 
should be installed large enough for the total number 
of switches, which allows the use of one gang switch 
plate for all the switches instead of separate single switch 
plates for each switch. 

Outlets for drop cords are made in the same manner 
as straight electric fixture outlets, care being taken to 
have the pieces of circular loom near enough together so 
that the concealed work rosette will cover the loom and 
holes. 

Outlets for floor and baseboard receptacles should have 
the wires and circular loom carried through in a manner 
similar to that for a ceiling outlet; and after the car¬ 
penter’s work is done the switch box may be fitted 
into the board, the wires and loom put into the holes and 


CONCEALED KNOB AND TUBE WIRING 


93 


the receptacle installed. The above described type of 
floor and baseboard receptacle is approved only in resi¬ 
dences and places that are not considered damp. For 
floors subject to dampness, the wires should be run in 
rigid conduit and receptacles of a waterproof type in¬ 
stalled in a water-tight box. 

When rigid conduit is used in mixed concealed knob 
and tube work, the rules for rigid conduit must be com¬ 



plied with. All conduits must be grounded as described 
in Chapter V. Where live wires pass through rigid con¬ 
duit except from a box, a fitting having a separate bush- 
hole for each conductor must be used for terminating the 
conduit and there must be no splice joists or taps in the 
fitting. The usual method is to use a fitting which screws 
to the conduit, called a condulet. They are made for all 
sizes of conduit and with any number of holes up to 80. 
Figure 63 and 64 show how they may be used. 

Cellar or Basement Wiring. — Outlets in a cellar or 
basement are usually for drop cords, which drop cords 
should be made with weatherproof sockets as a protec¬ 
tion to life. If a metal socket is installed in a cellar and 


















94 


PRACTICAL ELECTRIC WIRING 


the ungrounded wire of the system happens to make 
contact with the metal of the socket and a person who 
is standing on the ground touches this socket, the cur¬ 
rent will pass through the person’s body to the ground. 
The seriousness of the shock depends on the condition 
of the ground and the contact at the socket. With a low 



resistance contact between the hand and the wire and a 
good wet ground connection, a very severe shock may be 
obtained on only a uo-volt circuit. 

The wiring in the cellar is usually made to conform to 
the rest of the house; the wires are carried on the sides 
of the joists and through the joists, as previously ex¬ 
plained. 

In crossing the joists in a cellar, the wires are some¬ 
times run on knobs on the underneath side of the joist.*, 







































CONCEALED KNOB AND TUBE WIRING 95 


in which case, however, guard strips are required beside 
the wires to protect them from mechanical injury. 

Outlets in an attic are wired similarly to those in a 
cellar, except for the socket, which may be of the metal 
type instead of porcelain. 

Tests .—Tests are seldom made on the roughing-in 
wiring of concealed knob and tube work, as there is little 
likelihood of finding trouble. However, in a large or 
very important installation it is sometimes wise to make 
a thorough test. The test on an installation of this kind 
should be for short circuits and open circuits. With a 
magneto or bell and battery, ring across every pair of 
wires leading out from the cabinet box, as explained 
in Chapter IV. If the bells do not ring, the circuits are 
free from short circuits. To test for open circuits, con¬ 
nect the wires from the magneto or bell and battery to 
the wires of a branch circuit, short-circuit the wires at 
the outlets one at a time and, if the bells ring when each 
outlet is short-circuited, the wiring is free from open 
circuits. 

Completing the Job .—After the building is completed, 
the floors laid, the plastering done, etc., a second trip to 
the job must be made to install switches, cut-outs, drop 
cords and to make final tests. Fixtures are usually not 
included in the contract with the electrical contractor and, 
therefore, are not hung by the wireman, but are usually 
bought from a local fixture house, which has them hung 
without charge to the customer. However, for those who 
may be called on to install fixtures, the methods for con¬ 
cealed knob and tube work will be given. 

Fixtures .—For a straight electric fixture, a canopy 
block, which has holes bored in it for the wires and loom 
to pass through, is secured to the outlet by wood screws 
long enough to pass into the cleat which has been in¬ 
stalled behind the laths. Upon the end of the fixture 
there is screwed a three-legged fitting called a crowfoot. 
Wood screws are passed through the feet of the crow- 


96 


PRACTICAL ELECTRIC WIRING 


foot, which secures the fixture in place. The usual fix¬ 
ture joint is made, the joint is soldered and taped with 



rubber and friction tape and the canopy is set against 
the block, as shown in Fig. 65. 







































CONCEALED KNOB AND TUBE WIRING 97 


To install a combination fixture upon concealed knob 
and tube work, the gas pipe leading to the fixture should 
be covered with tape or circular loom to insulate it from 
the wires, as shown in Fig. 66. An insulating joint 
should be used to insulate the fixture from the gas pipe, 
and a canopy insulator to insulate the canopy from the 
ceiling. The insulating joint must be of the combination 
fixture type, one which has an opening through it for the 
gas to pass. Canopy insulators are usually fiber and the 
one that is easiest to install is a fiber ring with a slot into 
which the canopy fits. 

Switches .—To install a flush switch the plaster is 


Flush SwFch 


U+ 




HK 





Leaf her Washers' Flush Switch Box 

Figure 67. 


scraped out of the box and the screw holes in the switch 
box at top and bottom are made accessible. The 
switch box is often set too deep into the plaster 
to permit the switch’s coming flush with the surface of 
the plaster when it is installed against the box. Where 
this is the case, the usual practice is to use the long screws 
that come with the switch to secure it to the box, and 
place leather washers on the screws between the switch 
and the box, as shown in Fig. 67, to make it extend the 
desired distance. When the switch used is the white and 
dark button indicating type, common practice is to mount 
the white button above the dark one. 

Other Fittings .—To install drop cords for concealed 
knob and tube work, apply methods used in open work. 

To install knife switches and cut-outs, see Chapter 

IX. 

Finally, to install the branch blocks, connect the wires 










9 8 


PRACTICAL ELECTRIC WIRING 


into the same and pass the wires out of the box for the 
meter connection. Each of these wires should be encased 
in circular loom long enough to reach from the box to 
the meter, though with this method of insulating the 
wires, the distance between the two should not be more 
than two feet. 

Final Tests .—The final tests on the system should be 
for short circuits and open circuits, which have been de¬ 
scribed. If any conduit is used in the installation, a test 
for grounds should be made as described in Chapter VI. 

II. Finished House.—The code requirements for 
concealed knob and tube work apply to both new and 
old houses, though in an old house different methods are 
sometimes necessary to make the installation comply with 
the code rules. 

Entering the Building.—To carry the mains into the 
house, the best method is to use conduit as described at 
the beginning of this chapter. In following this plan, 
however, it would probably be impractical to run the con¬ 
duit down in the outside wall and the next best method 
is to run the conduit down on the outside of the wall and 
through the wall into -the cellar to the cabinet box, as 
shown in Fig. 71, Conduit Work. 

Other methods for carrying the mains into the house 
may be employed, but where any less secure plan is used, 
the main-line “cut-out” should be nearer the point of 
entrance than it is in the described conduit system. 

Branch Circuits .—The branch circuit wires are encased 
in separate pieces of circular loom and are carried 
through the walls or partitions to the floors above. The 
circular loom should extend in continuous lengths from 
the last support below to the first support above. 

Wiring under a Floor .—To wire for lights on the first 
floor, the floor boards on the second floor are taken up 
to allow the wire to be passed to the different outlets. 
It is not necessary to take up many boards and, if the 
wireman uses the methods whVh will be described, and 


CONCEALED KNOB AND TUBE WIRING 99 

is careful, the boards may be removed and replaced with¬ 
out marring the appearance of the floor. 

The following plan of a small house (Fig. 68) shows 
the layout for wiring for lights on the first floor by re- 




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Figure 68. 


moving the floor boards and doing the wiring on the 
second floor. 

Pockets .—In order to bring the wires from the cellar 
to the second floor, it is necessary to take up a short 
piece of board near the wall or partition, called a pocket, 
at the point L. To open a pocket, find a board, if pos¬ 
sible, that has an end near the desired place, then .with 


5 

3 


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100 


PRACTICAL ELECTRIC WIRING 


a putty knife and hammer cut the tongue out on both 
sides of the board to the next joist. Now, by using a 
sharp-pointed keyhole saw and driving it with the palm 
of the hand into the slot made with the putty knife, at 
right angles to the grain, and working it carefully back 
and forth, it may gradually be forced entirely through 
the board without first boring a hole which would after¬ 
wards be unsightly. Saw the board ofif close to the 
joist. Remove the board by prying it up with a putty 
knife or floor chisel. After the pocket is open, the wires 
are inserted in the knobs and the knobs are secured to 
the joists with nails and leather heads. 

In passing the wires under the floor boards parallel to 
the joists, the former practice was to encase the wires in¬ 
dividually in circular loom and fish them through. Be¬ 
cause of the expense of the loom, this method has been 
abandoned. The latest method of crossing the floor is 
to take up pockets every four or four and a half feet 
and support the wires entirely on insulators, as shown 
at G, H and I. 

In passing the wires through the joists, it is necessary 
to take up.two floor boards for the entire length of the 
cross-joist run; see A, B and C. Where there are rooms 
on both sides of the hall these boards are usually taken 
up in the hall, as shown in A. 

Removing Floor Boards .—To take up these boards, 
cut out the tongue of the boards with a putty knife for 
the entire length of the run. In using a putty knife, care 
must be taken to select one that is not too hard and will 
not break too easily. Usually the cheaper ones serve 
the purpose better. Cut the tongue out between joists, 
but do not attempt to cut out the tongue at joists, 
as the nails will ruin the knife. 

Flush Switches .—To install a flush switch with con¬ 
cealed work in a finished house, first take up a pocket 
in the floor above the place where the switch is to be in¬ 
stalled, then drop a weight tied to a string down the par- 


CONCEALED KNOB AND TUBE WIRING ioi 


tition or wall to make sure there is no obstruction between 
the opening above and the switch outlet. Next, locate 
the studding by tapping on the plaster. This is done to 
avoid the possibility of cutting out for a switch and find¬ 
ing a studding directly underneath. Having decided upon 
the location of the switch, bore a hole in the plaster 
round which the box hole is to be cut. The hole for this 
switch box must be cut so that the ears at top and bottom 
will rest on a lath or part of a lath. If this does not 
make the box rigid, wooden strips may be placed behind 
the laths and fastened to them with wood screws and the 


Branch Wires 0 O B(xture 


- 0 -^ 0 -* Switches 

Figure 69. 


box supported by them. The wireman should be very 
painstaking in cutting for a switch, to avoid making the 
hole so large that the switch plate will not cover it. The 
holes round the box, and all other holes that the wireman 
has made, should be filled. Plaster of Paris is usually 
used for this purpose, as it is very easily and quickly 
worked. ' 

Fixtures .—With a ceiling outlet for a fixture, a board 
should be nailed to the joists above the laths to bear 
the weight of the fixture, as previously described in this 
chapter. 

At the flush switch outlet, shown in Fig. 68, there are 
three instead of four wires carried to the two switches, 
thus saving one length of wire and loom to the switch. 
This is done by carrying one side of the line down to 
feed both switches, as is shown in Fig. 69. 

The wiring of the other floors of the building would 







102 


PRACTICAL ELECTRIC WIRING 


be done in the same manner as the one shown in Fig. 68. 

After the wiring is finished, the floor boards must be 
left up until the electrical inspector has inspected the 
"roughing-in” job. 

Replacing Floors .—After the installation has been ap¬ 
proved by the inspector, the floor boards are laid, and 
any remaining work on the job is finished. Eight- or ten- 
penny finishing nails are usually used to secure the floor 
boards in place. To lay the board that has been taken 
up for a pocket, it is first necessary to nail a cleat on the 



floor joist at one end of the board to support the board, 
as shown in Fig. 70. The board is then nailed to the floor 
joist at one end and to the cleat at the other. 

Final Tests .—As a precautionary measure, tests for 
short circuits and open circuits may be made at this 
time. The tests for short circuits and open circuits are 
described in Chapter IV. If three-point switches are 
used in connection with the installation, they should be 
tested as they are installed. 

Inspection .—After the wireman has completed the in¬ 
stallation, it is then necessary to have a final inspection 
made. 



















CONCEALED KNOB AND TUBE WIRING 103 


QUESTIONS. 

I. NEW HOUSE. 

1. When should the wires be installed for concealed knob 

and tube work in a new house? When should the 
fittings be installed? 

2. What distance must be kept between the wires when run 

on knobs? 

3. Explain a plan for making a service entrance with rigid 

conduit. 

4 . How must porcelain tubes that carry wires be placed 

in floor joists? 

5. Explain a labor-saving plan for drilling holes in floor 

joists. 

6. Explain a quick method of threading the wires through 

joists and inserting the tubes in the holes. 

7. What additional insulation is required where wires 

pass concealed from one floor to another? 

8. Explain two plans for securing split knobs. 

9. How should wires be run parallel to studding joists or 

rafters? 

10. Explain the method of making an outlet for a drop 

cord. 

11. Explain the method of making an outlet for (a) straight 

electric fixture; (b) combination fixture. 

12. Explain the method of installing a switch box for a 

flush switch. 

13. When should gang switch boxes'be used? 

14. What type of outlet box is commonly used for a base¬ 

board or floor outlet? 

15. Why should insulating sockets be used in cellars or 

damp places? 

16. Explain the method of installing a straight electric fix¬ 

ture on a concealed knob and tube work job. 


II. FINISHED HOUSE. 

1. Describe a plan for carrying service wires into a house 
with exposed conduit. 


104 


PRACTICAL ELECTRIC WIRING 


2. How are the wires usually insulated in the walls or 

partitions where they pass from one floor to an¬ 
other? 

3. How are the ceiling outlets on a floor wired for? 

4. Describe a method of taking up a board for a pocket 

in a floor. 

5. How are the wires insulated when they pass parallel 

to joists ? ' 

6. Explain the method of taking up floor boards for cross¬ 

joist wiring. 

7. Explain the method of installing a flush switch in a 

finished house. 

8. How is a ceiling fixture outlet made? 

9. How may the number of wires to be carried to a gang 

switch outlet be reduced? 

10. What must be done to make the wiring accessible to the 

inspector? 

11. How should the end of a floor board be supported when 

it does not rest on a joist? 


Exercises for Practice. 



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106 


















































































CHAPTER VI 


RIGID CONDUIT 

Rigid conduit is a specially constructed iron pipe, which 
usually has a protective coating of enamel on both out¬ 
side and inside. The external diameter is the same as 
for gas or water pipe of the same so-called size, but, 
owing to the thinness of the wall of the conduit, its 
internal diameter is a little greater. Conduits are similar 
to gas and water pipes, but in no case are wires approved 
when run in these instead of conduit. 

Rigid conduit wiring has the following advantages for 
most purposes : first, because the wires are protected from 
mechanical injury by the rigid metal of the conduit; sec¬ 
ond, should a short circuit or an arc occur in the conduit, 
there is little likelihood of its spreading to the building; 
third, if the wires show defects between the outlet boxes, 
it is an easy matter to draw them out and insert others. 

Concealed and Open Conduit. —The conduit may be 
either concealed or exposed. Where appearances are 
important, the conduit should be concealed. The method 
of carrying the mains into the house in this case is shown 
in Fig. 55 in Chapter V. 

Entering the Building. —The following arrangement 
(Fig. 71) is a standard method of carrying the mains into 
a house with exposed conduit wiring. 

As shown in Fig. 71, the conduit should have a bend 
of almost 180 degrees to form what is called a “drip 
loop” to prevent water from passing down the pipe. The 
fitting used where the wires pass into the conduit has 
the trade name of A13 condulet. Each letter and figure 
of the code of marking has a meaning in regard to the 

107 


\ 


I 


108 PRACTICAL ELECTRIC WIRING 

size, style and number of holes in the condulet. In this 
case, A signifies a straight type, I means a -J-inch con- 












































RIGID CONDUIT 


109 


duit, and 3 means that the porcelain bushing has three 
holes. Any supply house catalogue will enable the wire- 
man to select the condulet for the particular place de¬ 
sired and also furnish further information in regard 
to the system of marking. It is recommended that the 
service condulet extend out at least one foot from the 
building and, where practical, the condulet should be at 
least twenty-five feet above the ground. 

Pipe straps are placed on the pipe as a support, as 
shown in Fig. 71. They should be secured to wooden 
surfaces with wood screws and placed near enough to¬ 
gether to make the conduit secure. Good practice is to 
place them not more than six feet apart on straight runs. 

It would be less expensive to make a bend in the con¬ 
duit where it passes into the house instead of using the 
L condulet shown in the figure; however, the condulet 
makes a neater job. The cover for the condulet is a 
closed or blank cover; that is, it is of metal and has no 
openings for wires. Outside work is considered the 
same as a damp place, and extra precautions should be 
taken to keep water out of the pipe. The cover of the 
L condulet used should have a rubber gasket placed 
under it to exclude moisture. The pipe threads, where 
they pass into couplings, condulets, etc., should be painted 
with white lead or similar substance that will make the 
joint water-tight. 

Where the service pipe passes into the cabinet box, the 
plan used at all pipe-to-box connections should be em¬ 
ployed. The pipe should have threads cut on it with a 
standard stock and die, and the burrs on the inside of the 
pipe should be removed with a reamer or round file. 
After being fitted with a lock nut, the pipe is installed 
in the hole of the box. Then a bushing is screwed upon 
the end of the pipe inside the box, and the lock nut and 
bushing are screwed together until they grip the box 
firmly. This not only makes a good job mechanically, but 
insures good electrical contact between the conduit and 


no 


PRACTICAL ELECTRIC WIRING 


the box, which is necessary for grounding the metal 
conduit of the system. 

Wiring for Meter. —The wires for the meter may be 
carried out of the box through one large porcelain box 
bushing or through separate bushings and may be passed 
in circular loom to the meter; or, if the run is long, it is 
advisable to use a conduit and pass the wires through a 
condulet at the end of the conduit. 

The conduits, shown at the bottom of the box, after 
being threaded and secured into the box with lock nuts 
and bushings, as previously described, are carried to the 
outlets throughout the building. 

Tools Used.—The following is a list of tools necessary 
for installing conduit: 

\ 

i pipe vise 

1 stock with a set of dies 

2 pipe wrenches 

i pipe reamer or round file 
i pipe cutter or hack saw 
i pipe bender 
I ratchet brace 
I i-inch bit 

1 steel fish tape, 50 to 75 feet long 

2 screw drivers, large and small size 
1 compass saw, 14-16 inches long 

1 claw hammer 

1 gasoline or alcohol blowtorch 
1 pair 7-inch pliers 
1 i-inch wood chisel 
1 -^-inch twist drill 
1 can of oil for dies 

Preparing Conduit for Use.— One of the first things 

to be done in starting a conduit job is to find a suitable 
and convenient place to install the pipe vise. The pre¬ 
paring of the conduit for use on the job is done at the 
vise; therefore it should be handy. As the work pro- 


RIGID CONDUIT 


in 


presses, lengths of conduit must be cut and threaded to 
pass into the boxes, couplings, condulets, etc. 

In being cut, a piece of conduit is placed in the pipe 
vise and is cut off with a wheel pipe cutter or hack saw. 
For a job of ordinary size, the hack saw is usually pre¬ 
ferred, because it is lighter to carry. When a hack saw 
is used, care should be taken to avoid passing the saw 
too rapidly through the pipe, as the heat thus generated 
is apt to ruin the blade. 

After the pipe is cut, the next step is to ream the sharp 
burrs left from the cutting, out of the inside of the end 
of the conduit. This is done so that the sharp edges of 
the burr will not injure the insulation of the wires when 
they are pulled into the conduit. With the pipe still in 
the vise, threads are cut on it with the stock and dies. As 
the threads are being cut, oil, preferably lard oil, must 
be applied to lubricate and preserve the temper of the 
dies. The threads should extend on the pipe from J inch 
to i inch; however, the wireman is soon able to judge 
from experience the number of threads it is necessary 
to cut. 

Bending Conduit. —There are several methods of mak¬ 
ing bends in rigid conduit, three of which will be de¬ 
scribed. One is with a regulation wheel bender, which 
has attached to a lever a wheel which rolls the conduit 
round a surface of the desired curve. This device is too 
heavy to* warrant its use on small jobs. 

Another method, a temporary makeshift, however, is 
to bend the pipe with the aid of a stationary bender. 
Among the various plans to be employed, the following 
are the most practical. One is to bore a hole in a piece 
of timber a little larger than the pipe end and, using the 
length of pipe as a lever, bend it into the required curve. 
Another application of the same method is to fasten two 
cleats to a surface and make the bend, as shown in 
Fig. 72. 

In making a bend in this manner it is wise to bend 


112 


PRACTICAL ELECTRIC WIRING 


the pipe only a small amount at a time, and to pass the 
pipe backward or forward through the cleats until the 
required curve is obtained. 



The third method, the one most used, is to use a tee- 
pipe bender, commonly called a “Hickey.” They are 
made in different sizes for different-sized pipe, but the 


/ 


Figure 73. 

one used generally for bending |-inch pipe is made by 
screwing a piece of i^-inch pipe into a ij-inch tee, as 
shown in Fig. 73. To make the handle of the bender fit 















RIGID CONDUIT 


ii3 

the hand better a short piece of J-inch pipe may be 
screwed to the end of the ij-inch pipe with a ij-inch 
to J-inch reducing coupling as shown in Fig. 73. 

To make a bend by this method the conduit to be bent 
is passed through the tee, as shown in Fig. 73, and is 

.— 

Figure 74. 

placed on the floor. Standing with both feet on the 
conduit, the operator pulls or pushes on the handle of 
the bender to make the desired bend. The entire bend 
should not be made at one pull, as the sharp edges of 
the tee will kink the conduit, but short pulls should be 



made on the bender, slipping it along between pulls to 
avoid kinking. The Code states that the radius of the 
inner curve of the bend must not be less than 3^ inches, 
though, as a general rule, it is only necessary to see that 
















PRACTICAL ELECTRIC WIRING 


114 

no kinks are made in the conduit. As to the number of 
bends, the Code specifies that the conduit shall not have 
more than the equivalent of four quarter bends from 
outlet to outlet, the bends at the outlet not being counted. 



Offsets.—Where the conduit passes from one plane to 
another, or around an obstruction, a bend is required, 
called an offset, as shown in Fig. 74. 

This requires bending the conduit in opposite direc¬ 
tions and making the bends at different places. The 
first bend may be made with the tee bender in the usual 
way, and the second bend is made most easily with the 
bender, by allowing the curve of the conduit to extend 
































RIGID CONDUIT 


115 

down from an abrupt step, such as from a bench or porch, 
and then bending the conduit up in the usual way, on the 
higher plane, as shown in Fig. 75. 

The methods of doing concealed and open-conduit wir¬ 
ing are very similar, but each has some rules and meth¬ 
ods that differ. In open conduit wiring the conduit is 
installed, the wires drawn in, and the fittings installed 
immediately. In concealed conduit work the conduit is 
installed during the process of construction of the build- 


r<3 single po/e sw/tch 


Wires fd fixture 
in stalled fo box. 


7$ other /iqhts 


T'rom cabinet b 0 X 

Fig 

ing, but the wires must n< 
installed until the building 

J 

URE 

at b 
is 

To waft bracket 

77 - 

e fished in nor the fittings 
completed. 


The preceding diagram (Fig. 76) shows the method of 
wiring one room with concealed conduit in a house of 
frame construction. 


When the conduit passes parallel to the floor joists, 
it is secured to the side of the same with pipe straps or 
pipe hooks. 

When the conduit passes across the joists, the joists 
are notched with a saw and wood chisel, and the conduit 
is placed so that it lies just below the upper surface of 
the joists. Where supports are required for the con¬ 
duit in these notches pipe hooks are usually used. 

Outlet. —The outlet or junction box usually used in 










n6 


PRACTICAL ELECTRIC WIRING 


conduit work has five punchings in the bottom that may 
be knocked out for pipes to be inserted in the holes. 
These punchings for knock-outs are placed one in the 
center and four round the edge. The center hole is 
meant for the gas pipe to pass through, or for some other 
support to be placed in. The wireman will probably 
save himself considerable inconvenience if he makes 
it a rule never to pass a conduit through the 
center hole in the bottom of the box. The conduits that 
pass into the box must be threaded, and held firmly in 
place with a lock nut on the outside and a bushing on the 
inside of the box. 

Supporting Outlet Boxes and Fixtures .—There are 
several methods of supporting the outlet boxes and the 
fixtures attached to them. When the conduits that enter 
the bottom of the box do not interfere, the box is some¬ 
times secured to a wooden board nailed between the 
studding or joists. If a fixture is to be hung to this 
box a small fitting called a fixture stud should be se¬ 
cured to the bottom of the box before it is installed. 
This fitting is similar to a crowfoot with the exception 
that the nipple is male instead of female. The fitting is 
secured to the bottom of the box with short bolts called 
stove bolts. When properly installed this makes an ex¬ 
cellent support for a fixture. 

When an outlet box is installed in connection with a 
gas outlet, the box is held in place by securing it to the 
gas pipe with a fitting called a ‘‘dead ground box sup¬ 
port/’ The fitting is placed over the center hole, and 
secured to the bottom of the box with stove bolts. After 
passing the box and the box support up round the pipe 
to the desired height, a screw in the side of the box 
support is tightened, causing a nut to be pulled in against 
the pipe that locks box and pipe together. The fixture 
is of course hung from the gas pipe, which extends 
through the box. 

If an outlet has no gas pipe passing into it, gas pipe 


RIGID CONDUIT 


n 7 

or conduit is sometimes installed similarly to a gas pipe 
outlet, as shown in Fig. 78. 

Three short pieces of pipe are screwed into the tee. 
The pipe passing down to the outlet has threads cut on 
it for three or four inches, which allow the box to be 
held in place with a lock nut on each side of it, and also 
furnish threads on the pipe to support the fixture. Two 
other applications of this method may be made. One is 
to use instead of a tee, a fitting called a box hanger 
loop, which has the vertical pipe threaded into it, while 
the horizontal pipe simply slides through. The other 


Z' Pip e fe-c. 



Figure 78. 


is to use the “dead ground box support” to support tins 
box instead of using the two lock nut method previously 
described. As to the space to be allowed for lath and 
plaster to make the front of the box come flush with 
the same, the usual practice is to install the box so that 
its front edge will extend three-fourths of an inch from 
the front side of the joists. 

In installing boxes in concealed conduit work, it must 
be remembered that all outlet, junction, and switch boxes 
must be accessible after the building is completed. That 
is, they must not be installed where the inside of the box 
cannot be reached for fishing the wires, making joints, 
etc. 






















Ii8 


PRACTICAL ELECTRIC WIRING 


The “BE>” flush switch boxes used with conduit are 
installed in the same manner as the “AA” flush switch 
box described in Chapter V. 

Outlet boxes, installed for wall brackets, are usually 
secured to a board nailed behind them, and have a fix¬ 
ture stem fastened to the center of the box to support the 
fixture. 

Damp Places. —Where conduit wiring is done in damp 
places such as cellars, damp rooms, bathrooms and out¬ 
side places, the joints at the couplings, condulets, and 
similar fittings should be made water-tight with white or 


/Vo/ /s 


ll 


S/?<7ce tor 
Concrete, or 
h o // o kV fi/e 


\L 


Figure 79. 


red lead. The sockets and receptacles installed in these 
places should be porcelain or other insulating material 
for a protection to life, as described in detail on page 93. 

Fireproof Buildings. —In buildings of fireproof con¬ 
struction where the sub-floor is to be concrete or hollow 
tile much time will be saved if the wireman will install 
outlet forms where the outlets are to be located. These 
forms, which are usually made of galvanized iron, are 
tubular in shape, and have an internal diameter of about 
4J inches. 

These forms are nailed to the framework, as shown 
in Fig. 79, before the concrete is poured or the tile is 
laid into place. After the sub-floor is laid, the iron tube 
is then taken out, leaving through the floor a neat hole 
in which the outlet box and conduits may readily be in¬ 
stalled. The conduits between outlets in a building of 








RIGID CONDUIT 


119 

fireproof construction are commonly laid on the sub-floor 
over which the main floor is placed. 

Grounding Conduit Systems. —The metal of a conduit 
system must be grounded to a gas pipe, water pipe, or 
other suitable ground before the job is inspected. A 
ground must be made to a gas pipe only on the street 
side of the meter, while the ground to the water pipe may 
be made anywhere in the building. Where there is 
neither gas nor water pipe in the building, a pipe or rod 
may be driven into the ground and the ground wire at¬ 
tached to it. The surface of the ground pipe must have 
the scale or paint removed to insure good contact. As 



Ground Clamp. 


the conductor to ground, usually No. 10 B & S gauge 
wire is used, which is large enough for grounding con¬ 
duits when the largest wire in the system is not larger 
than No. o B & S gauge. The connection of the conduit 
and pipe is made with ground clamps, which may be pur¬ 
chased for any size of pipe. 

In the selection of the location for grounding it must 
be remembered that the ground clamps and the ground 
wire must be visible after the building is completed. 
Usual practice for grounding a conduit is to select a 
place in the building where the conduit and water pipe 
run near each other. The pipes are scraped clean of any 
insulating material where the ground clamps are to be 
placed. The wire is then cut long enough to reach be¬ 
tween clamps, and its ends are soldered into the lugs of 
the clamps, after which the wire and clamps are secured 
in place. The wire is soldered into the lugs before they 
are installed. Heat should never be applied to the lug 
while it is connected to the conduit. 


120 


PRACTICAL ELECTRIC WIRING 


If the distance between lugs is short, the wire may 
be passed from one to the other without supports; how¬ 
ever, with greater lengths, the wire must be treated as a 
conductor of the system and passed on insulators or in 
rigid conduit. 

Usually one ground connection is all that is necessary 
for an installation. Whenever there are two separate 
parts to a conduit system that are not connected, or can¬ 
not readily be connected, each part must be grounded. 

o 



Figure 8o. 

When a wooden cabinet box is used or the metal con¬ 
tact broken by some other means, the conduits are some¬ 
times bonded together with ground clamps and No. io 
copper wire. 

After the conduit and the boxes are installed and the. 
system is grounded, the work should be discontinued 
until the building is completed. 

Fishing Wires through Conduits. —One of the first 
things to be done when time comes to resume work on 
the installation is to fish the wires through the conduits. 
For this purpose a steel fish tape is usually employed, 
although, for short runs, duplex wire may be passed 
through without the aid of the “snake,” as it is sometimes 
called. 

To fish the wires through the conduit with fish tape 
the end of the tape is bent back to form a hook, so that 
it will readily pass the bends in the conduit. The tape is 
then pushed through from one outlet to another, and 
wires are secured to the tape and pulled through. In 
securing the wires to the tape the joint should be made 
as small as possible, so that it will pass easily through 
the conduit. The usual practice is to make a hook in the 
end of the tape, scrape the insulation from the ends of 



RIGID CONDUIT 


121 


the wires, and tie them into the hook, as shown in 
Fig. 80. 

Friction tape is then wrapped over the joint and pow¬ 
dered talcum or soapstone is applied to the tape to 
make it pull more easily. For long pulls in hot 
weather, because the insulating compound comes through 
the braid of the wire, it is frequently found necessary 
to use soapstone, or some other powdered lubricant, on 
the wires before they are pulled into the conduit. At 
least six inches of free wire should be left at every 
outlet and junction box for tapping on with other wires, 
and for making joints. 

Sometimes the wireman may find that the steel fish 
tape will not pass through the conduit, due to a com¬ 
bination of a long run, some short turns, and possibly 
a loose-fitting coupling. To get the tape through, use an 
additional tape, with a hook turned on the end; pass it 
into the distant end of the conduit, hook it into the end 
of the first tape inserted, and pull it through. If care is 
taken to screw the ends of the conduit till they meet in 
the coupling there is little likelihood of trouble in fishing 
the tape through. 

The National Electrical Code specifies the maximum 
number and sizes of wires that may be run in different 
sized conduits. The tables taken from the .Code will 
be found in the Appendix. 

Except in the case of stage pocket and border circuits 
(in theatre 'work) the same conduit must not contain 
more than four two-wire or three three-wire circuits of 
the same system except by special permission from the 
inspection department. (See Appendix Tables for 
Conduit.) 

Wires of different systems, that is an alternating cur¬ 
rent and a direct current system or from any two differ¬ 
ent supply systems, must never be run in the same con¬ 
duits. This is to make inspection and maintenance easier 


122 


PRACTICAL ELECTRIC WIRING 


and to prevent trouble on one system being communi¬ 
cated to the other. 

The joints made at outlet and junction boxes are 
usually made with the rat-tail splice, which is described 
in Chapter II. The joints are then soldered and taped 
with rubber and friction tape, are pushed back into the 
box, and the cover is secured in place. 



Figure 8i. Figure 82. 


Installing Fixtures. —To install drop cords on a con¬ 
duit system the round outlet box called an 8B box is 
usually employed. It has a cover, called a bushed cover, 
which has a hole drilled in it and threaded for a f-inch 
hard-rubber bushing. The drop cord is passed through 
the bushing, and the wires are knotted and taped to form 
a support for the cord, as described fully in Chapter IV. 
The drop cord wires are joined to the branch wires in the 
box by the fixture splice explained in Chapter II. 

To attach a straight electric fixture to a box in con¬ 
duit work an insulating joint must first be screwed to 
the stem or pipe. On this is screwed a fitting called a 
“hickey,” through which the wires pass to the inside of 
the fixture, as shown in Fig. 81. 

For combination fixtures an insulating joint is used 


















RIGID CONDUIT 


123 


that has an opening for the gas to pass through. It is 
merely an insulating coupling between the gas pipe and 
the fixture. The fixture wires are passed down between 
the casing and the gas pipe of the fixture. The canopy, 
with either type of fixture, should be insulated from the 
ceiling, as described on page 96. 

The final tests on the installation should be for short 
circuits, open circuits and grounds. The methods for 
testing for short circuits and open circuits were described 
on pages 69, 70, and 95. 

Test. —To test for a ground, secure one wire from 
the magneto or bell and battery to a clean bright place 
on the pipe or box, and touch the other wire to one wire 
leading out of the cabinet box. If, when the crank of 
the magneto is turned, the bells ring, there is a ground 
on that wire; but if the bells do not ring, the wire is 
free from grounds. Each wire leading from the cabinet 
box should be tested in this manner. If there are any 
switches that open any of the wires on the branch cir¬ 
cuits, they should be closed to make a reliable test. 


QUESTIONS. 

1. What advantages are to be gained by using rigid con¬ 

duit ? 

2. Explain in detail the best method of bringing the service 

into a building by rigid conduit. 

3. What distance should be allowed between supports for 

rigid conduit? 

4. Explain in detail the method of making rigid conduit 

water-tight in damp places. 

5. Explain the method commonly employed for securing 

rigid conduit in an outlet ox. 

6. How are the wires passed out of a switch or cabinet 

box to the meter? 

7. Make a list of the tools necessary for installing conduit. 

8. In using a hack saw for cutting lengths of conduit, what 

should be avoided? 


124 


PRACTICAL ELECTRIC WIRING 


9. How are the burrs reamed out of a conduit, and why is 
this necessary? 

10. In the use of a stock and die, what should be done to 

preserve the temper of the dies? 

11. Describe three methods of bending rigid conduit. 

12. How many quarter bends does the code allow between 

outlets? 

13. How is an offset made in rigid conduit? 

14. When may the wires be drawn and the fittings installed: 

(a) I11 open conduit wiring? 

(b) In concealed conduit wiring? 

15. Explain the method of passing concealed rigid conduit 

across and parallel to joists in a building of frame 
construction. 

16. For what should the center knock-out hole in a round 

outlet box be reserved? 

17. Explain two methods of installing outlet boxes for 

straight electric fixtures. 

18. Explain the method of installing an outlet box for 

a combination fixture. 

19. Describe in detail the use of forms for outlet boxes in 

fireproof buildings. 

20. How are outlet boxes installed for wall brackets? 

21. Explain in detail the method of grounding the metal of 

a conduit system. 

22. How are wires drawn through the conduit? 

23. Explain the method of installing a straight electric 

fixture to an outlet box. 

24. Explain the method of installing a combination fixture 

on a conduit system. 

25. Explain the method of testing a conduit system with 

a magneto for short circuits, open circuits, and 
grounds. 


JOO/J. U/OJJ. UQ 


Exercises for Practice. 


\ 



























































126 



















































CHAPTER VII 


ARMORED CABLE AND METAL MOLDING 

I 

1/ Armored Cable. —Armored cable consists of two 
spiral windings of metal tape round a diameter of about 
half an inch, which forms a flexible protection for the 
wires. Usually wiring is done with a cable called “BX,” 
in which the wires are inserted. This “BX” may be pur¬ 
chased loaded with different numbers and sizes of wires. 
The one commonly used contains two No. 14 wires. The 
ordinary “BX” may be used in places that are not con¬ 
sidered damp; for damp rooms, cellars and outside places 
a cable is required that has a lead sheath between the 
wires and the armor, known as “BXL.” Where condi¬ 
tions will permit the use of rigid conduit, however, “BX” 
is usually installed instead of “BXL,” because the expense 
is somewhat less. 

Armored cable is used simply as a. substitute for rigid 
conduit in concealed wiring, and the general rules and 
methods for conduit wiring apply also to wiring with 
armored cable. Switch outlets and junction boxes, fix¬ 
ture supports and ground clamps are of the same type, 
and are installed in the same manner as in a rigid con¬ 
duit system. 

Use of “BX” in Finished House .—Though wiring with 
armored cable is done in new houses, around machinery, 
etc., it is more commonly used for wiring finished or old 
houses. In wiring a finished house with “BX” the main 
wires are usually brought into the cabinet box in exposed 
rigid conduit, as shown in the chapter on conduit work. 
From this cabinet box the branch circuits are run with 
“BX,” with the exception of those that are run in the • 

127 


128 


PRACTICAL ELECTRIC WIRING 


cellar. Where it is necessary to wire across the cellar 
before the cable is fished up to lights above, the common 
practice is to install a junction box where the “BX” 
leaves the cellar, and to run conduit over to it from the 
cabinet box. The box, of course, serves as a coupling 
between the conduit and the cable, and furnishes a place 
to join the wires. . 

For runs of cable of ordinary length in walls, parti¬ 
tions, or between floors, supports are not required, the 
cables being simply fished through and installed at the 
outlet boxes. Where the cable is run open, pipe straps 
to fit the cable should be used generously to make a neat 
appearance. 

Securing Cable to Boxes .—When a cable passes into 



Figure 83. 


a cabinet, outlet, or junction box, the cable must be 
firmly secured to the box for grounding purposes, and 
some kind of bushing must be provided to protect the 
wires from the sharp edges of the cable. Outlet boxes 
may be purchased that have a combined bushing for the 
wires and clamp for the cable. At cabinet boxes, and 
where the ordinary conduit boxes are used, a cable-to- 
box connection is required. The connection, which is 
called a “Hood” connector, has some method of clamping 
the cable, and a lock nut and shoulder to clamp the box, 
as shown in Fig. 83. 

Cutting Armored Cable .—In preparing the “BX” to be 
inserted into the “Hood” connector and into the box, 
about seven inches of the cable must be cut off, to allow 
wire for joints in the box. There are several cable cutters 
on the market for this purpose. However, a hack saw 


ARMORED CABLE AND METAL MOLDING 


129 


seems to be a more popular tool for this purpose. To 
cut the cable with a hack saw, it should be bent over 
something' and, while held firmly, the outer armor is 
sawed partly through, and is then broken by bending 
the cable back and forth at the joint. This done, the 
outer sheathing may be twisted toward the end of the 
cable, and the inner layer may be cut in the same manner. 
In using a hack saw to cut a cable care must be taken 
to prevent the hack saw’s passing through the cable and 
cutting the wires. Also, unless the cable is held securely, 
the cable may turn and twist the hack-saw blade into two 
pieces. For this purpose hack-saw blades with flexible 
backs may be secured, and they are considered less ex¬ 
pensive because of their lasting qualities. 

The cables must be continuous from outlet to outlet. 
If the cable between outlet boxes is to be spliced, it is 
necessary to install a junction box into which to pass the 
cables, so that the joints in the box will be accessible. 

Passing Cable under Floors. —“BX” is considered su¬ 
perior to concealed knob and tube work for wiring an old 
house, because the cable gives better protection to the 
wires and less work is required to install it. In passing 
the cable across floor joists, it is only necessary to take 
up one floor board instead of the two required for con¬ 
cealed knob and tube work. When the cable is passed 
parallel to floor joists no supports are required; therefore 
it is only necessary to take up pockets at the outlets and 
near the walls or partitions where the cable is to be fished 
down or up. 

Where the cable passes across joists, the cable must 
not be laid in notches cut in the joists, as is done for con¬ 
duit, because the nails from the floor boards are likely to 
pass into the cable and short-circuit the wires. Holes 
should be bored into the joists and the cable threaded 
through. For boring holes a f-inch bit should be used, 
and preferably one with a long shank. 

In fishing the cable parallel to joists under a floor 


130 


PRACTICAL ELECTRIC WIRING 


invisible obstructions may be encountered. A flashlight 
and a small hand mirror will assist the wireman in mak¬ 
ing an examination of the obstruction. 

When a mirror is held in the opening of the floor 
at the proper angle, it will reflect the light from the 
flashlight to the obstruction. 

Passing Cable through Partitions .—In fishing cables 
through walls or partitions, braces between the studding 
may be encountered. It usually requires considerable 
work to pass through or by such a brace, and a good 



plan is to select another location for the outlet, where 
the passage for the cables has no obstruction. How¬ 
ever, when it is necessary to locate the outlet at this par¬ 
ticular place, the cable may be carried to the box by one 
of the two following methods. In the application of the 
first method, the writer has in mind a place where there 
was a cross-brace in a partition, three or four feet above 
the first floor of the house. In this particular case a 
f-inch gas pipe about 4 feet long was used as an exten¬ 
sion to a long bit. One end was fastened to the bit and 
the other end was made square with a hammer and 
screwed in the brace. The bit was then inserted from 
the cellar into the passage, and a hole was bored into the 
cross-piece. Where conditions will permit, this is an ex- 
























ARMORED CABLE AND METAL MOLDING 131 


cellent method of making a passage through. The other 
method of passing the cable through the partition or wall 
is to pass the cable around the brace. If the obstruction 
is on the outside wall of a weather-boarded house, it is 
only necessary to remove three or four of the boards, 
and with a wood chisel cut a notch in the brace through 
which the cable may be passed. The exact height of the 
obstruction may be found by fishing a weight tied to a 
string from above. Where it is not practicable to reach 
the brace from the outside, it may be necessary to cut 
the plaster and pass the cable around the obstruction. 
If the wall is of white plaster it is only necessary to cut 
out the plaster opposite the brace, pass the cable around, 
and fill the hole with plaster of Paris. Where the wall is 
papered one or two plans for removing the paper may be 
used. If water will not fade the color of the paper a 
cross is cut in the paper at the place where the opening 
must be made. Then, with a sponge or rag, warm water 
is applied to the paper to loosen the paste. This will 
allow the four pieces of paper to be opened, as shown 
in Fig. 85, so that the plaster may be removed. 

After the cable has been passed around the brace, the 
hole is filled with plaster of Paris, and the paper is pasted 
back into place. 

Where paper may be secured to match the paper on 
the walls, the paper over the hole is usually cut out with 
the plaster, and when the hole is filled new paper is 
inserted over the hole. 

Fixture Outlets .—As previously stated in this chapter, 
the outlets for concealed “BX” wiring are made in a 
similar manner to those for concealed conduit. However, 
a different type of outlet box is usually employed for 
fixture outlets. Instead of installing the deep “8B” box, 
used with rigid conduit, a shallow box of the same 
diameter and about \ inch deep is used. The plaster 
is cut out at the outlet to fit- the box, so that the bottom 
of the box rests against the laths. This position of the 


I3 2 


PRACTICAL 'ELECTRIC WIRING 


box allows the canopy of the fixture, when installed, to 
fit neatly against the plaster. 

In a finished house that has been wired with armored 
cable, one inspection must be made before the floor 
boards are nailed into place. 

Open armored cable wiring is seldom done except' in 
connection with machinery. The cable, being small and 
flexible, is better for passing around the curves on the 
machinery to the motors and lights. 



II. Metal Molding .—Metal molding is generally 
used in connection with conduit, and it was probably 
designed and manufactured as a substitute for rigid con¬ 
duit. When properly installed, it makes a much neater 
job than does open rigid conduit, therefore it is gen¬ 
erally used instead of exposed conduit, where appear¬ 
ances are a consideration. 

Metal molding is like wooden molding, in that it has a 
backing and a capping. The backing is secured to the 
surface wired Over, and the capping is usually held to 
the backing by a spring catch arrangement. 

Wires in Molding .—The Code specifies that metal mold¬ 
ing must not be used for circuits requiring more than 
1,320 watts of energy; therefore, wiring with metal mold¬ 
ing is confined almost entirely to branch circuits. Even 
branch circuits are seldom run with metal molding en¬ 
tirely, as conduit is always required in passing through 
floors, and is sometimes required in passing through par¬ 
titions. There are several types of molding on the mar- 








ARMORED CABLE AND METAL MOLDING 


133 


ket, but the one generally used has a hacking over which 
a capping is snapped, as shown in Fig. 86. 

The molding comes in ten-foot lengths, and the 
hacking has holes in it about 2 feet apart, through which 
the screws are passed which hold it in place. 

If the molding is received with the backing and capping 
snapped together, the most satisfactory way to separate 
them is to hook the screw hole in the hacking over a 
nail and pull off the capping. # 

The backing is first installed and the wires are laid in 





Figure 86 . 


place, and the capping is then snapped over the backing. 

Cutting .—Where it is necessary to cut the lengths of 
molding, it is cut with a hack saw, a three-cornered file, 
or a ‘"hand shear.” In cutting the molding with a hack 
saw, a fine-tooth blade known as a tube saw should be 
used. A fine-tooth blade does not catch or stall in the 
molding, which allows it to work easier, with less liabil¬ 
ity of its breaking. By using care, the cutting may be 
done with the ordinary hack-saw blade, but fewer blades 
will be broken if a blade with a tempered edge and flex¬ 
ible back is used. 

To cut the molding with a three-cornered file, each 
side of the piece of backing is marked deeply with the 
file, and is then broken into two pieces. A short piece of 
capping is sometimes used as a straight-edge guide for 
the file, as shown in Fig. 87A. 










134 


PRACTICAL ELECTRIC WIRING 


The hand shear has a cutter attached to a lever, which 
cuts off the backing- or capping at one stroke, as shown 
in Fig. 87B. This is the fastest method and is used 
on large installations. 

Supports .—Metal molding is supported by screws or 
bolts passed through countersunk screw holes in the base 




B 

Figure 87. 


of the backing. Different surfaces require different sup¬ 
ports and some of these will be suggested. 

For wood surfaces, use a i-inch No. 8 flat-head wood 
screw, as shown in Fig. 88A. 

In lath and plaster, use a 1 J-inch No. 8 flat-head wood 
screw, as shown in Fig. 88B. This holds securely if the 
screw goes into the lath, but where it misses the lath 
some other means of support must be arranged. If the 








ARMORED CABLE AND METAL MOLDING 135 


molding runs across laths another hole may be drilled in 
the backing about a half-inch away, which should cause 
the screw to enter the center of the lath. In drilling 
this hole, as well as any other holes in the molding for 
screws, it must be remembered that all screw holes must 
be countersunk, so that the screw heads will lie flush with 
the inner backing surface. 

If the metal molding runs parallel to the laths and it 
is impossible to hit a lath with a screw, the next best 
thing is to drill a larger hole in the plaster and insert a 
toggle bolt, as shown in Figs. 88D and E. 

On metal ceilings a -J-inch cone-head toggle bolt, 2 
inches long, is suggested, as shown in Fig. 88C. 

Where the plaster is laid on a metal lath, a T-head 
toggle bolt, size -J inch, 2 \ inches long, as shown in Fig. 
88D, is suggested. 

On plastered tile surfaces either of the two toggle 
bolts mentioned may be used. 

On brick or concrete two methods of supporting the 
molding are suggested, for either of which it is necessary 
to drill a hole with a star drill or cold chisel. The most 
common method is to drive a wooden plug into the hole 
and saw it off flush with the surface; then the screw that 
holds the backing is driven into this plug. Another 
method, which is considered superior by some, is to use 
an expansive screw shield or expansive bolt, as shown in 
Fig. 88F. 

Bonding Lengths .—In the installation of metal mold¬ 
ing it must be remembered that the lengths of molding 
xfiust be connected together at all joints and fittings for 
the purpose of grounding the metal for the entire system. 
For this purpose base couplings, as shown in Fig. 89A, 
may be secured. Still the following method, which is 
approved, may be of value to the wireman. Cut the sides 
of the backing off so that its base will lie upon the other 
length of backing and allow the screw holes to come 
together, as shown in Fig. 89C. Then a wood screw, 


136 


PRACTICAL ELECTRIC WIRING 


passed through the two holes and into the surface wired 
over, will bond the two lengths of molding together. 
Use of Important Fittings .—The adjacent lengths of 



Figure 88 . 


molding must be electrically connected through fittings 
as well as through couplings, and for this purpose the 
fittings that are to be inserted in a line of molding must 
have metal bases with small machine screws, under which 
the ends of the backing may be secured. 



A 



—1 

O 

1- 

0 

1- 

- 

B 


c 



Figure 89. 


Where it is necessary to run one or two lines of 
metal molding at right angles from a point in an exist¬ 
ing or proposed run, a metal molding tee or cross, as 
shown in Fig. 90, must be installed at this point. These 






















































ARMORED CABLE AND METAL MOLDING 


137 


tees and crosses not only serve as a neat connection be¬ 
tween the runs of molding, but also serve as a junction 
box where joints in the wires may be made. The 90- 
degree flat elbow, shown in’Fig. 90, is for making right- 




Figure go. 


angle turns on flat surfaces with metal molding. The 
cover of this elbow has also a recess like the tee and cross, 
which allows room for making joints in the wires. The 
remaining elbows shown in Fig. 90 will be of much assist¬ 
ance to the wireman in making neat turns. Ffowever, 
joints in the wires should not be made in them, as there 
is not room for proper taping. 

Mitering .—Instead of using the. elbows for making 
turns metal molding is sometimes mitered with a hack 



PRACTICAL ELECTRIC WIRING 


138 

saw to form the desired angle. A “V”-shaped piece is 
cut out of the inner side of the turn of the backing, 
leaving the outer side as the hinge of the turn. The 
capping is then cut to fit the' backing and laid into place 
after the wires are installed. The mitered turn must 
make good electrical connection between the two lengths 
of molding and, where this conductivity is not maintained 
with a part of the backing left intact, a short metal strip 
should lie under the backing and be secured in place by 
wood screws that pass through both the backing and the 
strip. Mitered turns, though not used often, have an 
advantage in that they fit the corners of right-angle turns 
more snugly than do the purchased elbows. For curved 
surfaces, or other places where it is desirable, metal 
molding may be bent. By using care it may be bent for 
any radius down to inches. Bends should be made 
with the backing and capping snapped together, but be¬ 
fore the wires are installed. 

On irregular surfaces there is sometimes a tendency 
for the backing and capping to spring apart. With the 
lype of molding shown the capping may be made to 
grip the backing more firmly by hammering on the sides 
of the capping with a wood mallet. Where this is not 
sufficient the backing and capping may be held together 
with the strap clamps shown in Fig. 92, which may be 
bought for this purpose. 

Passing through Floors .—In a metal molding installa¬ 
tion, where the circuit is to be passed through the floor, 
it is necessary to use a piece of -J-inch rigid conduit. 
Usual practice is to use a length of pipe which extends 
through the floor and for three inches above the floor, 
though where the mechanical strength of the molding 
above is considered inadequate the conduit must extend 
five feet above the floor. In connecting molding to con¬ 
duit or iron boxes the couplings shown in Fig. 91A are 
usually employed, though the corner box shown in Fig. 
91B is also often very useful for this purpose. 


ARMORED CABLE AND METAL MOLDING 139 


Passing through Partitions .—In passing through par¬ 
titions the rigid conduit, required for passing through 
floors, may be omitted, and the molding may be passed 




B 

Figure 91. 

directly through, providing the partition is dry and the 
molding is in continuous length, with no joint or coupling 
within the partition. In passing through partitions that 
are considered damp rigid conduit is required; neverthe- 


140 


PRACTICAL ELECTRIC WIRING 


less, this requirement seldom needs to be enforced, as 
metal molding' is not approved for damp places. 

After the backing is installed the wires may then be 
laid into place and the capping snapped on. Single-braid, 
rubber-covered wire is approved, and is usually used as 
the conductor. For alternating current systems the two. 
or more wires of the circuit must be installed in the same 
molding, and this is also recommended for direct current 
systems. The Code does not limit the number of wires 



Figure 92. 


to be placed in a line of metal molding. If single-braid 
wire is used, where it is desirable as many as four wires 
may be placed in the molding. 

Joints or splices made in the wires may be made at 
tees, crosses, or other fittings, but should not be 
made in the molding between fittings. All joints must, 
as with other metallic systems, be soldered and taped 
with both rubber and friction tape. 

Grounding System .—To ground a metal molding sys¬ 
tem use a ground clamp similar to Fig. 92, and apply 
the rules and methods for grounding conduit. 

Final Tests .—The tests on the installation should be 
for short circuits, open circuits, and grounds, as de¬ 
scribed for conduit work; on pages 69, 70, 95, and 123. 

As with all open work installations, the request for 
inspection should be made after the job is finished. 





ARMORED CABLE AND METAL MOLDING 141 


QUESTIONS. 

I. ARMORED CABLE. 

1. What is armored cable? 

2. Where is “BX” approved, and where is “BXL” re¬ 

quired? 

3. For what class of wiring is armored cable adapted? 

4. How is armored cable held in place where it passes 

into iron boxes? 

5. How should you cut off lengths of armored cable? 

6. In concealed armored cable wiring, how is the cable 

carried: 

(a) Parallel with joists? 

(b) Across floor joists? 

7. Explain a good plan for examining obstructions between 

joists under floors. 

8. Describe in detail two methods of passing a cable 

through or around a brace in a partition. 

9. In wiring for ceiling outlets with armored cable in a 

finished house, what type of box should be used and 
how should it be installed? 

xo. Fbr this class of wiring, when should requests for in¬ 
spection be made? 

II. METAL MOLDING. 

1. How many watts of power are permitted by the code 

on a circuit run in metal molding? 

2. What is the order of installing the backing, capping, and 

wires ? 

3. What precautions should be taken in cutting metal 

molding with a hack saw ? 

4. How are lengths of metal molding cut with a three- 

cornered file? 

5. How should metal molding be supported on the follow¬ 

ing surfaces: 

(a) Wood surfaces? (b) Plaster over wood laths: 

(c) Plaster over metal lath? (d) Plaster over^tile? 
(e) Metal ceiling? (f) Brick or concrete? 


142 


PRACTICAL ELECTRIC WIRING 


6. Explain two methods of bonding lengths of metal mold¬ 

ing together. 

7. Explain the method of taking a tap circuit from a run 

of metal molding. 

8. Explain the method of mitering metal molding instead 

of using the elbow fittings. 

9. How should bends in metal molding be made? 

10. How are the backing and capping held together where 

there is a tendency to spring apart? 

11. How is metal molding carried through: (a) Floors? 

(b) Partitions? 

12. What kind of insulated wire must be used in metal 

molding? 

13. Should metal molding be grounded? 

14. What tests should be made on a metal molding in¬ 

stallation? 


Exercises for Practice. 


Ouf/efs for Fijtfa res 




o Q 













































































144 









































































US 























































































CHAPTER VIII 


SPECIAL WIRING 

Systems of Distribution. —In interior wiring the 

lamps or current-consuming devices are almost always 
connected in multiple, that is, across the two wires. The 
branch wiring is then practically always the same for 
any installation. The main and feeder wiring, however, 
may differ because of the nature of the current supplied 
or of the number of wires used. 



Figure 93. 


Two-Wire System .—The most common service for in¬ 
terior wiring is to use only two wires from the source 
to the centers of distribution, as shown in Fig. 93. 

This service is used for a line which furnishes either 
direct or alternating current having a potential of no 

146 






























SPECIAL WIRING 


147 


volts. It may be used as well when the potential dif¬ 
ference between wires is 220 volts, hut it is unusual to 
use a 220-volt service, because ordinarily the lamps and 
apparatus are designed for no volts. 

Three-Wire System .—The three-wire service shown 
in Fig. 94 is used quite extensively for three-wire direct 



Figure 94. 


current and three-wire, single-phase, alternating current 
circuits. Though three wires are required they need 
to be only half the size of those required on the two- 
wire system to supply the same load, provided it is 

balanced. 

Three-Wire Convertible System .—In some instances 
the customer specifies a three-wire convertible system; 
that is, the system may be so wired that it may be com 
verted into a two-wire system without changing any of 
the wiring. To do this, it is only necessary to use a 










































148 


PRACTICAL ELECTRIC WIRING 


neutral wire twice as large as one of the outside wires, 
instead of using one of the same size. Then when the 
system is changed from a three-wire to a two-wire the 



Figure 95. 


neutral is used as one wire and the two outside wires 
are connected and used as the other wire, as shown in 

F >g- 95- . 

A system wired in this manner may be changed from 


/.care/ 


To sSfreet 


/Vlcr/nS- 



r* 


Geftercrfo r 


Figure 96. 


one source of power to another by using a double-throw 
switch. For instance, in a building that is equipped with 
a two-wire generating plant, where a three-wire service 
of the city power company is also desired, a three-pole, 
double-throw switch would be used, as shown in Fig. 96. 


















































SPECIAL WIRING 


149 


With this connection, however, the fuse in the central 
pole of the fuse block, on the right-hand side, will be 
double the capacity of the others. 

Four-Wire, Two-Phase System .—A four-wire, two- 
phase, alternating current service is not often used as 
such for lighting purposes. The power company’s mains 
in the streets may carry such currents for motors and, 
therefore, it may be found convenient or necessary to use 



Figure 97. 


these mains for the lighting load. Where the lamp load 
is small, perhaps below six or eight kilowatts, the interior 
wiring is done with a two-wire system and the main 
wires are tapped to one phase. If the lamp load is very 
large, a four-wire service is carried into the building, 
and the load is divided between the two phases, as shown 
in Fig. 97. 

Three-Wire, Three-Phase System .—Small lamp loads 
to be connected to three-phase, three-wire circuits are 
usually wired as two-wire systems, having the main wires 
connected to two wires of the three-phase in the street. 
Small towns are often wired with this system by balanc¬ 
ing the load across each phase. 


















































PRACTICAL ELECTRIC WIRING 


150 

Meter Loops. —Ordinarily it is not the duty of the 
wireman to install the electric meter, but wires should 
be arranged for connection to the meter. This arrange¬ 
ment is commonly called the meter loop. The meter is 
always connected between the main switch and the branch 
blocks, and the loop is made differently for different 
systems. 

Two-Wire System. —The usual meter loop for a two- 
wire system is shown in Fig. 93. A loop that is rather 
unusual, but will serve for any two-wire meter, is shown 
in Fig. 98. 

Three-Wire System. —For three-wire, direct current, 


Mete r 


\ t 


Figure 98. 

or three-wire, single-phase, alternating current, the wires 
that pass into the meter may be either four or five in 
number, depending upon whether the potential circuit is 
to be connected across 220 or no volts. Usually the 
potential for three-wire alternating current meters is de¬ 
signed for 220 volts, and the meter loop for such a meter 
is made as shown in Fig. 94. The potential for a three- 
wire, direct-current meter is commonly connected across 
110 volts, and the meter loop is made as shown in Fig. 99. 

Four-Wire, Tzvo-Phase System. —For a four-wire, 
two-phase meter, one wire of each phase is connected 
through the meter, and a wire is connected to the other 
wire of each phase, as shown by the meter loop in Fig. 97. 

Three-Wire, Three-Phase System. —For a three-wire, 
three-phase meter, two wires are connected through the* 















SPECIAL WIRING 


151 

meter, and the third wire has a tap taken off for poten¬ 
tial, as shown by connections in Fig. 99. 

Switch Suggestions. —Single-pole switches are used 
almost entirely for controlling lamps on branch-circuit 
wiring, though in some instances it may be desirable, or 
even necessary, to use double-pole switches. Single-pole 
switches may be used to control lights on a circuit of 
no volts potential, where the current broken is not more 
than five amperes, if the wires are not likely to become 
grounded. Double-pole switches should be used to con- 


0 0 0 




T C 



Meter 


5 ' A 

Figure 99. 


L oad 


trol lamps where the load is large, or where it is large or 
small if the wires are located in a damp place. 

In metallic systems, such as rigid conduit, armored 
cable or metal molding, it is considered much better 
practice to place the switch in the ungrounded wire, 
as shown in Fig. 100. 

Should a high resistance ground develop on the wire 
between the switch and the load, it cannot draw current 
when the switch is open. 

Pendant Switches .—Pendant switches, suspended by a 
lamp cord, are often used in controlling lights. The 
usual pendant switch is single pole and is connected to 
one side of the line leading the load. As a substitute for 
a pendant switch, a key or pull-chain socket with a fuse 
plug screwed in it will serve the purpose. 

In the wiring of cut-outs or fuse blocks it is recom- 






















152 


PRACTICAL ELECTRIC WIRING 


mended that the shells of the block be connected on the 
load side, to prevent the possibility of a short circuit 
across the shells when the fuse plugs are removed. 

Three-Point and Four-Point Switches. —Three-point 
and four-point switches are used quite extensively in 
controlling lights from two or more different points; that 
is, regardless of the position of the other switches, the 



Figure ioo. 


lights can be turned on or off from either switch. For 
two points of control, such as the stairway control, the 
three-point switches are commonly used, as shown in 
Fig. ioi. Two of the points of a three-point switch are 
strapped together and they must be connected to thv' 
single wire leading to the source or to the load. 

Any number of points of control may be added by con- 



Figure ioi. 


necting four-point switches between the three-point 
switches, as shown in Fig. 102. In the connection of 
these, one of the two wires passing through all the 
switches must be cross-connected at each switch. 

Three-point switches cannot be used anywhere except 
on the end position for independent control, but four- 
point switches may be used for the intermediate or end 
positions. Fig. 103 shows the connections for two four- 




















SPECIAL WIRING 


153 


point switches used on the end positions instead of the 
three-point switches. 

Often in residences the hall lights on the first and 



second floors are controlled by three-point switches, re¬ 
quiring four switches and six, five, or four wires between 
the switches. Where there is no effort made to save 
wire, six wires are connected as shown in Fig. 104. 



The usual practice is to connect the switches as shown 
in Fig. 105, and thereby eliminate one wire. 

As shown in Fig. 106, only four wires are used be' 


0 

- 0 - 

0 

H-rk_AH 


HA 


Figure 104. 

tween the switches, but this plan is only possible where 
the same circuit has been carried to lights, on both 
floors. This arrangement may be used on non-metallic 
systems such as open wiring (knobs or cleats), wooden 





































154 


PRACTICAL ELECTRIC WIRING 


molding or concealed knob and tube work, but it should 
not be used in rigid conduit, armored cable or metal mold¬ 
ing, because of induction troubles that may arise. Fur¬ 
ther reduction in the number of wires between switches 



Figure 105. 


may be made only by connecting both sides of the line 
into a switch, which method is not approved. 

Tests. —Three-point and four-point switch connections 
should always be tested after they have been installed. 
As the switches are usually installed before power from 
the lighting company is available, a bell and battery or 



a magneto is commonly used for testing these circuits. 
To test the circuits with a magneto connect the wires 
from the magneto to the branch wires and install the 
lamp at the outlet, or bare the wires and twist them 
together. Turn the crank of the magneto and the bells 


































Figure 107. 


155 




































PRACTICAL ELECTRIC WIRING 


156 

should ring every second change in the position of any 
of the switches in the circuit. 

The three-point and four-point switches may be pur¬ 
chased in either the flush or the snap type. The flush 
switch makes a neater appearance where it is possible 
to install it. 

Stairway Control Systems. —A stairway control sys¬ 
tem for a number of floors is shown in Fig. 107. 

As to its operation, the turning of the first-floor switch 
lights the lamps on the first and the second floors; the 
turning of the second-floor switch lights the lamps on the 
third and extinguishes the first-floor lamps; the turning 
of the third-floor switch lights the lamps on the fourth 
floor and extinguishes the lamps on the second floor; 
the turning of the fourth-floor switch lights the lamps 
on the fifth floor and extinguishes the lamps on the third 
floor; and the turning of the fifth-floor switch extin¬ 
guishes the lamps on the fourth and the fifth floors. The 
reverse takes place on the down trip. Two serious ob¬ 
jections are made to this system; first, the turning of a 
switch out of order will cause the lamps to light out 
of their proper order; secondly, when the switches have 
been operated on the up-trip they must be operated again 
on the down-trip before the lamps will light in order for 
the next up-trip. 

Double-pole switches are used on the first and fifth 
floors, three-point switches are used on the other floors. 

A more expensive, though a much more satisfactory, 
system of stairway control is shown in Fig. 108. Two 
switches must be turned at each landing to operate the 
lights on the floors above and below, instead of one used 
in Fig. 107, but the selective control of the lights, which 
this gives, more than offsets this disadvantage. The 
switches on the first floor will control the first- and the 
second-floor lights, the switches on the fourth floor will 
control the fourth- and the third-floor lights, and the 
switches on each of the other floors will control the light 



157 





































































158 


PRACTICAL ELECTRIC WIRING 


on that floor, on the floor below, and on the floor above. 
This system is always “set" for operation, and the turn¬ 
ing of any switch will operate the lamp on that circuit 
regardless of the position of the other switches. Two 
three-point switches are used on each floor with a four- 
point added on the second and the third floors. 

Electrolier Switches. —Two-circuit and three-circuit 
electrolier switches are used in controlling separate lamps 
or separate groups of lamps in an electric fixture. They 
may be purchased in either the snap or the flush type; 
the only difference in their operation is that one has a 
key to be turned while the other has a plunger to be 


Figure 109. 

pushed. One quarter-turn of the three-circuit snap switch 
lights one lamp or group of lamps; the second quarter- 
turn lights the second lamp or group of lamps; the third 
quarter-turn lights the third lamp or group of lamps; and 
the fourth quarter-turn cuts off the current from all 
lamps. Fig. 109 shows the wiring of a three-circuit 
switch used with a three-light fixture. 

The two-circuit switch, as the name implies, is like the 
three-circuit switch except that it controls two lamps, 
or groups of lamps, instead of three. 

Burglar Circuit. —In residence wiring a very desir¬ 
able feature known as the burglar circuit is sometimes 
added. By its use, in case of an alarm in the night, 
the entire house may be flooded with light by closing 
one switch. There are separate switches for controlling 
such lamp, or group of lamps, and one master switch that 
turns them all on or off. Three-point switches are used 
at the individual control points and a single-pole switch 









SPECIAL WIRING 


159 


is used at the master control point as shown in Fig. no. 
The individual switches must be in the off position before 
the lamps can be controlled by the master switch. 

In connecting these three-point switches the wire com¬ 
ing from the lamps must connect to the two points in the 
switch that are strapped together, while the other two 
wires may be connected interchangeably to the other two 
contacts. 

Remote Control Switches. —Sometimes the customer 
"O 
O 


3 Point 

Switch as 


Master 
Switch ^ 

Figure no. 

specifies a point of control for a large number of lamps 
remote from the main switch. This may be accomplished 
by using the solenoidal switch shown in Fig. hi. 

The remote control switch may be an indicating, single¬ 
pole snap or flush switch. If other points of control are 
desired three-point or three- and four-point switches may 
be employed instead of the single-pole switch. 

Safety Switches .—Where machinery is driven . by 
motors it is sometimes desirable to have several points 
throughout the building from which the main switch may 
be opened in order to stop all the motors. The remote 
control switch shown in Fig. hi may be used for this 
purpose, but a much less expensive switch may be de- 


<2ES> <$S> <H> 































i6o 


PRACTICAL ELECTRIC WIRING 


vised. Fig. 112 shows an arrangement whereby the 
blow from a falling weight upon a lever will open the 
switch. The tripping arrangement for the weight may 
be made with a lever and the coils and armature of an 
electric bell, arranged as in the plan shown. Two to four 
cells of battery are sufficient to operate the trigger, and 
buttons may be placed in convenient places. 


So/enoic/s 



^Tank Switches. —Motors connected to a pump for 
supplying water to a tank are usually controlled auto¬ 
matically by a tank switch. There are several tank 
switches on the market which open and close the circuit 
by the action of a float. They are manufactured in both 
single- and double-pole and give different ranges of 
water height. In the wiring of a motor and a float switch 
there should be a switch near ,the motor to cut off the 
current to switch and motor and another switch arranged 
to put the motor on the line, independent of the float 



























SPECIAL WIRING 


161 


switch. This may be accomplished by using a double¬ 
pole, double-throw knife switch in connection with a 
single-pole float switch, as shown in Fig. 113. 



Small alternating current motors, that is, up to two 
horsepower, are usually connected directly across the line, 



while larger motors require resistance or reactance in 
the circuit. If a D. C. motor larger than one-quarter 












































162 PRACTICAL ELECTRIC WIRING 

t 

horse power, is used, a solenoidal or other form of remote 
starter must be used. 

Fittings for Bathrooms and Damp Places. —As ex¬ 
plained in another chapter, there is danger of an electric 
shock where metallic sockets or fixtures are installed in 
bathrooms, cellars, or any place where a person may 
come into contact with the ground while touching them. 
To avoid this danger, insulating sockets of porcelain or 
composition are used where their appearance is not ob¬ 
jectionable. Also metallic fixtures are often placed high 
enough to be out of reach from the floor, and are con¬ 
trolled by wall switches. If, for special reasons, metal 
fixtures must be used and must be placed within reach 
from the floor, they should be grounded. In a bathroom 
this can easily and neatly be done by grounding the wire 
to the fixture and carrying it concealed to the ground on 
the water pipe. The commercial ground clamp makes 
the best connection to ground and should be used where 
conditions will permit. 

Locating Troubles. —When a fuse plug on an exist¬ 
ing branch circuit of wiring burns out, it is usually due 
to a short circuit or dead ground. The following is the 
method usually employed to locate and correct the trou¬ 
ble. If the system is a metallic system, or one in which 
there is any likelihood of a ground, remove both fuse 
plugs and screw a lamp into the socket of one of them. 
.If the lamp burns, there is a ground on that wire, and 
it is most probably in a junction or outlet box. The 
connection in these boxes should be examined, and when 
the ground is opened the lamp will be extinguished. 
Should the lamp not light when screwed into one socket, 
it should, of course, be removed and be inserted into 
the other socket for the same test. This lamp method 
would show only low resistance grounds. The test for 
high resistance grounds must be made with a voltmeter 
or magneto. 

Short Circuit .—To locate a short circuit screw a good 


SPECIAL WIRING 


163 


fuse plug and a lamp in the cut-out, as shown in Fig. 114. 

Turn off all the lamps and current-consuming devices 
on that circuit. If there is a short circuit, the lamp will 
remain lighted until the short circuit is removed. The 
most probable places where the short circuit will be found 
are where the wires are joined in the junction or outlet 
boxes, and are connected under binding screws in fixtures, 
rosettes and sockets. 

Where it seems impossible to locate the short circuit 
by this method, because of the large number of poorly 
insulated connections, the circuit is sometimes sectional- 


f Lamp 

f@h 


Cf 


O 




^Fus 


Figure 114. 


ized. The circuit is opened near the middle, or between 
weak points, and the two parts thus divided are tested 
separately to determine on which of them the short cir¬ 
cuit exists. It may be necessary to open the circuit wires 
and perform tests even a second or a third time to make a 
satisfactory location of the trouble. To illustrate, sup¬ 
pose that, in Fig. 114, the lamp burns, indicating a short 
circuit, and that, after opening the wires at a and b, 
the lamp is extinguished. This of course indicates that 
the wires between the cut-outs and a and b are free 
from short circuits. Then suppose the wires to be recon¬ 
nected at a and b, and to be opened at b and c, the lamp 
will then indicate whether or not there is a short circuit 
between a and b and b and c. This testing by sections 
can be carried on until the' exact point is located, but 
usually this is not necessary, as the probable trouble is 
evident 







164 


PRACTICAL ELECTRIC WIRING 


The lamp method of locating a short circuit is the 
most convenient method, but, in rare instances, the lamp 
will not indicate the presence of a cross between wires 
because of its high resistance. In such cases it is neces¬ 
sary to use a magneto or to follow some other method 
of testing for high resistance contacts, and afterwards 
to perform the tests previously described. 


QUESTIONS. 


1. How are lamps or other current-consuming devices 

usually connected in interior wiring? 

2. Make a diagram for a 2-wire wiring system from the 

service entrance to the lamps, showing all necessary 
fittings. 

3. Make a diagram for a 3-wire single-phase alternating 

current system with all necessary fittings from service 
entrance to the lamps. 

4. What is the advantage of the 3-wire system over the 

2-wire system? 

5. What is meant by a 3-wire convertible system? 

6. Make a diagram of a switch for changing a 3-wire sys* 

tern to a 2-wire system. 

7. How may 2-phase alternating current be used for light¬ 

ing loads? 

8. How may a 3-phase alternating current service be used 

to supply power for lighting loads? 

9. Show by diagram the wiring for meter loops on the 

following systems: 

(a) 2-wire, A. C. or D. C. 

(b) 3-wire, with a 220-volt potential circuit. 

(c) 3-wire, with a no-volt potential circuit. 

(d) 4-wire, 2-phase. 

(e) 3-wire, 3-phase. 

10. What type of switch is generally used in controlling 

lamps on branch circuits? What is the current-carry¬ 
ing capacity of this switch for no volts? 

11. Where wires are carried in conduit, and one wire of 


SPECIAL WIRING 


165 

the system is grounded, where is it advisable to con¬ 
nect a single-pole switch? 

12. How are pendant switches usually connected in a line? 

Suggest a good substitute for a pendant switch. 

13. How may a fuse block be connected into a line to pre¬ 

vent possible trouble? 

14. What is the object of using 3- or 4-point switches? 

15. Make a diagram for controlling four lamps with two 

3-point switches. 

16. Make a diagram for controlling four lamps with two 

3- point and three 4-point switches. 

17. Draw a diagram for controlling two lamps from three 

different points, using only 4-point switches. 

18. Draw a diagram for the stairway control of two lamps, 

using four 3-point switches and five wires between 
floors. 

» 

19. Explain in detail a method of testing out 3-point and 

4- point switch connections before power is available. 

20. Explain the use and the operation of a 3-circuit snap 

switch. 

21. Draw a diagram for twelve lights controlled in fours 

by a 3-circuit switch. 

22. Draw a diagram for a burglar circuit in connection with 

four 3-light fixtures. 

23. Explain the use of the remote-control switch. 

24. Show by diagram an original method of opening the 

main switch to motors from several different points 
in a building. 

25. Make a diagram for controlling a pump motor with a 

double-pole tank switch and a double-pole knife switch 
near the motor, knife switch to operate the motor 
independently of the float switch. 

26. Mention three methods of preventing a person from 

receiving an electric shock from metallic sockets or 
fixtures in bathrooms or other places where the floor 
may be damp. 

27. Explain a method of locating and removing a ground 

on a lighting system. 

28. Explain the lamp fuse plug method of locating a short- 

circuit on a branch circuit. 


CHAPTER IX 


WIRING PRACTICE 

Factors. —In the lighting of a house, sometimes as 
many as four different companies have a part in the 
work, each with a different duty to perform. They are as 
follows: a plumbing contractor, an electrical contractor, a 
fixture supply house, and the power company. 

Duties. —The part of the work done by each factor 
may differ slightly in different localities. The writer 
gives the duties of each, based upon practical experience 
in wiring in Tennessee, Maryland and the District of 
Columbia. # 

It is the duty of the plumber or gas-fitter to install all 
gas pipes and locate gas outlets. 

It is the electrical contractor’s duty to do all the wir¬ 
ing in the house and install all drop cords, switches, base¬ 
board and floor receptacles, etc. 

' It is the duty of the firm supplying the fixtures to in¬ 
stall all fixtures and connect the fixture wires to the 
branch wires at the outlet. 

It is the duty of the power company to run service 
wires from the street to the house and make connections 
with the main wires that have been extended through 
the walls by the wireman. It is also the duty of the 
power company to install and connect the wires to the 
electric meter. In rare instances, the power company 
will wire into the main-line cut-out, but it is unusual for 
them to do any work inside the building. The con¬ 
tractor should carry his mains out through porcelain 
bushings and leave about twelve inches for connections 
with the power company’s wires outside the building. 

1 66 


WIRING PRACTICE 


167 


The contractor does not install the meter, but he must 
leave a place in the mains, between the entrance switch 
and the branch blocks, where the meter may be installed. 

The electric fixtures are usually supplied and installed 
under a separate contract, as the customer usually pre¬ 
fers to purchase them from a firm in the fixture business. 
In taking a contract, however, either verbal or written, a 
definite understanding should be had as to who is to 
supply and install the electric fixtures. 

Size of Mains. —In deciding on the size of mains to 
be used in an installation, it is usually only necessary to 
choose a wire that is large enough to carry the current 
without heating. 

The current to be carried by the mains is generally 
determined by the number of branch circuits. 

As specified by the Code, no branch circuit must carry 
more than 660 watts. Then, dividing 660 watts, the 
maximum load on a branch circuit, by no, the usual 
branch voltage, the quotient, 6, is the amperage of the 
branch. Then, to calculate the number of amperes that 
will pass over a main for a two-wire system, it is only 
necessary to multiply the number of branch circuits by 
six. Thus, if a two-wire system has connected two 
branch blocks, the current in the mains will be 2 X 6 or 12 
amperes. 

On a three-wire system, with a balanced load, as shown 
in Fig. 115, the current of e goes through wire a, then 
through b d to load f in series, and back to wire c, there¬ 
by requiring only six amperes for two branch circuits, 
instead of twelve, in a two-wire system. If the load is 
unbalanced, that is, if there are more branch circuits con¬ 
nected between b and a than between c and d, the excess 
of load on one side will return through the neutral wire g, 
as if it were a two-wire circuit. 

To calculate the current in the mains, add the number 
of balanced branch circuits, multiply by six, and divide 
by two. To this amount add the excess of current in 


PRACTICAL ELECTRIC WIRING 


168 

all branch circuits on one side over the balanced load. 
. This sum gives the total current in the mains. Thus, for 
a 5-branch circuit, where four are balanced and one is un¬ 
balanced, 4X6 = 24^2=12 amperes. 12 -j- 6 = 18 
amperes in wire c, while the neutral wire g will carry 
the difference, or six amperes. \ 

After knowing the number of amperes to pass over the 
mains, their size is usually selected by referring to the 


Z20E 


a 


110E 

9 

c 




<?> ftw 


6 d 


Figure 115. 



carrying capacities of wires, as stated in the National 
Electrical Code. As a convenience to the reader, the 
part of the table most commonly used is given on page 
169. Then, if by calculation it is found that the total 
number of branch circuits requires twelve amperes, a No. 
14 wire which carries fifteen amperes would be used as 
mains. A method frequently employed is to use two 
No. 14 wires as mains for a system having only two 
branches on a 2-wire system and three No. 14 wires 
as mains for a system having four branches on a 3-wire 
system. 

It is always necessary to use a wire for mains that will 
carry the current without heating, but the contract may 
call for a still larger wire. For instance, in a large in¬ 
stallation, the contract may specify that wires of suf¬ 
ficient size must be used so that, when all lamps are 








WIRING PRACTICE 


169 


“Allowable Carrying Capacities of Wires.” 

1913 Code 


B. & S. 

Rubber 

Insulation 

Other 

Insulation 

Circular 

Gauge 

Amperes 

Amperes 

Mils 

18 

3 

5 

1,624 

16 

6 

10 

2,583 

. 14 

15 

20 

4,107 

12 

20 

25 

6,530 

10 

25 

30 

10,380 

8 

35 

50 

16,510 

6 

50 

70 

26,250 

5 

55 

80 

33 ,ioo 

' 4 

70 

90 

41,740 

3 

80 

100 

52,630 

2 

90 

125 

66,370 

1 

100 

150 

83,690 

0 

125 

200 

105,500 

00 

150 

225 

133,100 

000 

175 

275 

167,800 

0000 

225 

325 

211,600 


turned on, the drop in voltage from the main line switch 
to the farthest lamp on the system shall not exceed 3 per 
cent. It is necessary to make a calculation to find the 
wire or wires required for mains and branches when the 
per cent, drop is specified. 

The following wire formula may be used for direct 
current and for 2-wire and 3-wire single-phase alter¬ 
nating current where the load is a lamp load or of some 
other non-inductive nature. If the load is inductive, 
motors or arc lamps, it is recommended that a. size be 
used which is 25 per cent larger than the one obtained 
from the wiring formula. 


CM = 


LX 22 XI 

e 


Where: 

L == length in feet one way 
I = current in amperes 



170 


PRACTICAL ELECTRIC WIRING 


e = volts lost in line 
CM — Size of conductor in circular mils 
22 = constant 

Example .—What size wire should be used on a 114- 
volt circuit when it is necessary to carry 70 amperes a dis¬ 
tance of 100 feet with a loss of 3 per cent under full 
load ? Three per cent, of 114 equals 3.42 volts which may 
be lost in the line. 


100 X 22 X 7 ° 
34 


= 45,294 circular mils 


• According to the table of allowable carrying capacities 
of wires, a No. 3 wire, which is the next heavier size, 
would be selected. As may be seen from the table of 
carrying capacity of wires, the wire selected is one size 
larger than would have been required by the Code. So in 
certain cases it may be necessary to use a larger wire 
than the Code calls for in order to prevent an exces¬ 
sive loss of potential in the line. On the other hand, a 



Figure 116. 













































WIRING PRACTICE 


171 


wire smaller than the Code requirement should never be 
used under any circumstances. 

In an interior wiring installation, the size of wire used 
and the current passing would probably differ in dif¬ 
ferent parts of the circuit. In an installation con¬ 
sisting of two cabinet boxes or distributing centers, a 
large wire would be used between the main switch and 
the first cabinet box, and probably a smaller wire would 
be used between the first and the second cabinet box, 
while probably a still smaller wire might be used on the 
branch circuit. 

As an example, suppose that with the wiring diagram 
shown in Fig. 116 the contract specifies not more than 
3 per cent, drop under full load from the switch to the 
farthest lamp on the circuit. If the voltage at the main 
switch is 114, then 3 per cent of 114 = 3.4 volts which 
may be lost in the line. This voltage drop may be divided 
among the different sections to suit the contractor. In 
Fig. 116, suppose we allow 1.4 volts drop between the 
switch and the first cabinet box, and 1 volt between the 
second and the third cabinet box, and 1 volt between the 
last box and last lamp on the branch circuit; then with 12 
branch circuits and 6 amperes to a circuit there are flow¬ 
ing between the switch and the first distribution center 
12 X 6 or 72 amperes. Using the formula 


40 X 22 X 7 2 
i -4 


= 45,255 c.m. or No. 3 wire. 


Between the first and second cabinet box 6 X 6 or 36 
amperes are passing. Then 

20 X 22 X 36 „ AT O • 

-— 15,840 c.m. or No. 8 wire. 


On the branch circuit we will suppose the center of 
distribution to be 30 feet from the cabinet box. 

Then, 

30 X 22 X 6 


1 


3,960 c.m. or No. 14 wire. 





172 


PRACTICAL ELECTRIC WIRING 


Then with No. 5 wire for the first part of the main, 
No. 8 for the second part and No. 14 for the branch, the 
drop would not exceed 3 per cent under any load. Where 
a change in the size of the main is made, a cut-out must 
be installed, unless the fuse installed for the larger wire 
will also protect the smaller. In Fig. 116 a cut-out should 
be installed at the first cabinet box to protect the run 
of No. 8 wire. Where the run of mains after passing 
the first cabinet box is short, usual practice is to continue 
the mains with the larger wire and thereby save the ex¬ 
pense and trouble of installing a cut-out. 

Branch circuits on all systems are wired with No. 14 
wire, except where the circuit is to be more than 100 feet 
long, when a No. 12 wire or larger size is generally used. 
This larger wire is employed to avoid too great a loss in 
candle power by the lamps at the remote end of the long 
circuit. 

Number of Lights. —The National Electrical Code 
permits as many as twelve 50-watt lamps, or sixteen 
sockets for 40-watt lamps, on one branch circuit; but 
in most instances it is considered better practice to wire 
for ten instead of twelve sockets on a branch. 

In residence wiring, some of the outlets have fixtures 
connected to them that have more than one light and the 
contractor should allow amply for these in laying out 
the branch circuits. When the contractor knows the 
number of lamps that are to be connected to an outlet, 
the outlet may be wired for the stated number of lamps. 
Otherwise, he should be guided by the rules that follow. 
The Code does not specify the number of lights allowed 
for different kinds of outlets. However, the following 
regulation, which prevails in the District of Columbia, is 
an excellent rule to follow: 

Parlor ceiling outlet. 4 lights or sockets 

Sitting-room ceiling outlet... 4 “ “ “ 

Dining-room “ u ... 4 “ “ “ 



WIRING PRACTICE 


173 


Living-room 

ceiling outlet. .. 

4 

lights 

or 

sockets 

Library 

a a 

4 

ii 

ii 

ii 

Reception hall “ “ ... 

3 

a 

ii 

ii 

Bedroom 

a a 

3 

a 

ii 

ii 

Bedroom toilet “ “ 

1 

light 

or 

socket 

Kitchen outlets. 

1 

ii 

ii 

ii 

Wall or bracket outlets. 

1 

a 

ii 

ii 

Hall 






Pantry 

Ceiling or wall 





Washroom 

outlets, each.. 

1 

ii 

ii 

ii 


Bathroom 

Plug outlets.1 ampere each 

Locating Outlets. —In locating the outlets in a resi¬ 
dence, the following rules, which are usual practice, will 
probably assist the wireman: 

Wall brackets in living-rooms, 5 feet 6 inches 
above the floor 

Wall brackets in chambers, 5 feet above the 
floor 

Wall brackets in halls and corridors, 6 feet 3 
inches above the floor 

Wall brackets in offices, 6 feet above the floor 

Snap and flush switches, 4 feet 2 inches above the 
floor 

Knife switches, 4 feet 6 inches above the floor 

Cabinet and switch boxes, 5 feet above the floor 

Sockets from drop cords, 6 feet above the floor 

Knife Switches. —In the mounting of knife switches, 
the Code specifies that they must be so placed that gravity 
will not tend to close them when the switch is open. The 
switch may be mounted so that the blades stand either 
vertically or horizontally, but when mounted vertically 
the hinges of the blades should be below, so that gravity 
will tend to open instead of to close the switch. 

Combination Switch and Cut-Out .—In the majority of 
small installations, the main line fuse block and the main 









174 


PRACTICAL ELECTRIC WIRING 


line switch are combined into one fitting, called a com¬ 
bination entrance switch and cut-out. In installing this 
fitting, the cut-out must be installed on the line side of 
the switch to protect it in case of a short circuit across 
the blades. Usually a combination entrance switch and 
cut-out is constructed for entrance from the top, as 
shown in Fig. 117A. Where the entrance is made at the 
bottom, it is usually necessary to turn the switch blades 
around, as shown in Fig. 117B. 



I J) c=Q=p 

I 


‘Hinges 


Figure 117. 


To turn the blade around, the sealing wax over the 
screw heads on the back side of the switch is broken out, 
the screws are removed and the positions of the jaws and 
blades are interchanged. 

In the mounting of knife switches, fuse blocks and 
branch blocks, the best practice is to inclose them in iron 
or wooden boxes. This is not required by the Code, 
ordinarily, and often the boxes are omitted where the 
inspector having jurisdiction does not require them and 
the customer wishes a cheaper job. Switches and cut¬ 
outs should be placed in boxes because the boxes protect 
them and make a neater appearance. 

Power Required for Illumination. —The amount of 
power required for general illumination may be ascer¬ 
tained by the use of the following table. 

The rule for the application of the table given below is 
as follows: 
















WIRING PRACTICE 


175 

Total watts = area of room in square feet X foot- 
candles X constant taken from table. 

For general illumination, 3 or 4 foot-candles are 
usually sufficient. 

As an example, a room 25 feet wide and 40 feet long, 
with a light ceiling and dark walls, is to have an illumi¬ 
nation of 3 foot-candles throughout. This illumination is 
to be obtained by the use of metallized filament lamps and 
prismatic reflectors. 

Substituting the area (1,000 square feet), the required 
foot-candles (3) and the proper constant (55), 

Total watts = 1,000 X 3 X -55 — 1,650. 

If 50-watt lamps are used, 33 will be necessary. 

To secure approximately uniform illumination, the 
light sources should be separated by a distance not greater 
than twice their height above the plane where the illumi¬ 
nation is desired. 

The following table shows the number of watts per 
square foot of floor area required to produce an aver¬ 
age of I foot-candle of illumination (Watts per lumen) : 

Tungsten Lamps rated at 1.25 watts per horizontal 
candle-power; clear prismatic reflectors, either 
bowl or concentrating; large room; light ceil¬ 
ings; dark walls; lamps pendant: 


Height 8 to 15 feet. 0.25 

Same with very light walls. 0.20 


Tungsten Lamps rated at 1.25 watts per horizontal 
candle-power; prismatic bowl reflector enameled; 
large room; light ceilings; dark walls; lamps 


pendant: 

Height 8 to 15 feet. 0.29 

Same with very light walls. 0.23 


Metallized Filament Lamps rated at 2.5 watts per hori¬ 
zontal candle-power; clear, prismatic reflector; 
either concentrating or bowl; large room; light 
ceiling; dark walls; lamps pendant: 


Height 8 to 15 feet. 0.55 

Same with very light walls . 0.45 








176 PRACTICAL ELECTRIC WIRING 

f i 

Carbon Filament Lamps rated at 3.1 watts per horizon¬ 
tal candle-power; clear prismatic reflector, either 
bowl or concentrating; light ceiling, dark walls; 
lamps pendant: 

Height 8 to 15 feet. 0.65 

Same with very light walls. 0.55 

Bare Carbon Filament Lamps rated at 3 * 1 watts per 
horizontal candle-power; no reflectors; large 
room; very light ceiling and walls: 

Height 10 to 14 feet. 0.75 to 1.5 

Same, small room, medium walls. 1.25 “ 2.0 

Carbon Filament Lamps rated at 3.1 watts per hori¬ 
zontal candle-power; opal dome or opal cone re¬ 
flectors; light ceilings; dark walls; large rooms; 


lamps pendant: 

Height 8 to 15 feet. 0.70 

Same ,with light walls. 0.60 

I 


Wooden Cabinet Boxes. —Wooden cabinet boxes 
were used extensively until recently. On account of the 
time required for the building of the box by the elec¬ 
trician, it is considered cheaper to use the iron box. For 
the benefit of wiremen in localities where wooden boxes 
are still used, suggestions for constructing them will be 
given. 

The wood used in the box must be well seasoned and at 
least three-fourths of an inch thick and must be thor¬ 
oughly filled and painted. The lining may be of J-inch 
slate, J-inch marble, J-inch approved composition or -J- 
inch asbestos. Except in large installations, asbestos is 
generally used. One-eighth inch asbestos is secured to 
the sides of the box with screws or tacks, generally the 
latter. The box should have a neat door and some means 
of fastening the door when closed. Wooden or compo¬ 
sition cabinets must not be used with metal conduit, ar¬ 
mored cable or metal molding systems. This require¬ 
ment is made mainly because the wooden box does not 
make a metallic connection between the different runs 








WIRING PRACTICE 


177 


of conduit, cable or molding that pass into the box, 
which connection is necessary for the grounding of the 
system. 

In a wooden cabinet box where the wires pass from the 
box, bushings or tubes through which they run to the 
connections, each wire should be encased in circular 
loom. Where such runs are short and the wires are not 
carried near other wires, loom may not be required; but 
where the runs are long, as from one side of the box 
to the other, or where they pass near other wires, all such 
wires should be encased in circular loom. 

In iron cabinet boxes, the wires may be passed to the 
fittings without being encased or supported in any way. 
Some inspectors make an exception to this implied rule 
and require circular loom on the wires for the longer 
runs, such as a run from the top to the bottom of the box. 

Insulation of Wire. —Wires with various kinds of 
insulation are sometimes permitted in different classes 
of wiring. Rubber-covered wire is now required almost 
entirely. It may be purchased with either single or 
double cotton braid; the former is cheaper but is not ap¬ 
proved for some wiring systems. 

Rigid conduit and armored cable systems require 
double-braid, rubber-covered wire, while single-braid, 
rubber-covered wire may be used in open-work wiring 
(cleats or knobs), concealed knob and tube work, wood 
molding and metal molding. 


QUESTIONS. 

1. Explain in detail the various portions of the work for 

which the plumber, power company and electrical con¬ 
tractor are responsible in wiring a house. 

2. How many watts of energy are permitted on a branch 

circuit? . 

3. What is the largest current ordinarily that flows in a 

branch circuit? 


i 7 8 


PRACTICAL ELECTRIC WIRING 


4. What usually determines the size of wire to be used for 

mains in any system? 

5. Explain the method of determining the size of wire to 

be used for mains with a given number of branch 
circuits: 

(a) For a two-wire system; 

(b) For a three-wire system. 

6. In a 2-wfre system with 84 lights and 7 branch cir- 

suits, how much current would be flowing in the mains 
under full load? What size mains would be required? 

7. In a 3-wire system with 84 lights and 7 branch circuits, 

how much current would be flowing in each of the 
three main wires under full load? What size mains 
would be required? 

8. State the current-carrying capacity for four different 

sizes of wire—rubber insulation. 

9. What is meant by a certain “per cent, drop” in a line? 

10. State the formula for determining the size of wire to 

be used with a specified drop in voltage. Indicate the 
meaning of the letters in the equation. 

11. What sized wires would be required on a 115-volt cir¬ 

cuit to furnish current for one hundred ^-ampere 
lamps a distance of 150 feet with a 4 per cent loss 
in voltage at full load? 

12. What sized wires would be used on a 2-wire circuit to 

carry 50 amperes a distance of 200 feet with a drop 
of 2 per cent if the voltage between the wires is 
225 volts? 

13. With three wires of the same size on a 3-wire, 115- 

and 230-volt direct current system, what size mains 
would be required to supply current to 200 ^-ampere, 
1 io-volt lamps a distance of 400 feet with a 4 per cent 
drop ? 

14. What sized wire would be used on a 115-volt wiring 

installation with one distribution center supplying 6 
branch circuits 150 feet from the main switch, allow¬ 
ing a 3 per cent, drop in voltage? 

15. What sized wire would be required for the same in¬ 

stallation, using three-wire 115- and 230-volt mains? 

16. Where should cut-outs be placed in main wires? 


WIRING PRACTICE 


179 


17. What size of wire is generally used on branch circuits? 

When is it advisable to use a larger wire? 

18. How many sockets are permitted on a branch circuit? 

19. What outlets in a residence should be wired for as if 

they were to have five sockets? 

20. What outlets should be considered to take current: 

(a) For three sockets? 

(b) For two sockets? 

(c) For one socket? 

21. • How high above the floor should wall brackets be placed: 

(a) In dining-rooms? 

(b) In chambers? 

(c) In halls? 

(d) In offices? 

22. What is the usual height of: 

(a) Flush switches? 

(b) Knife switches? 

(c) Cabinet boxes? 

(d) Sockets from drop cords? 

23. How should knife switches be mounted? 

24. How would a combination cut-out and switch, arranged 

for entrance from the top, be changed to an “enter 
from the bottom” fitting? 

25. How many 40-watt Tungsten lamps would be required 

to furnish an illumination of three foot-candles in a 
room 30 feet wide and 50 feet long, if the room has 
light walls and light ceilings, and the lamps are to 
be twelve feet above the floor? 

26. How many 50-watt, metallized filament lamps would 

be required in the foregoing problem? 

27. Explain imdetail the building of a wooden cabinet box. 

28. Should circular loom be used on the wires in wooden 

cabinet boxes? 

29. In what systems of wiring must double-braid, rubber- 

covered wire be used? In what systems may single¬ 
braid, rubber-covered wire be used? 


CHAPTER X 


WIRING FOR MOTORS 

Wiring Systems. —The wiring for motors may be 
installed with any of the systems used for lights. It 
should be remembered in this connection, however, that 
metal molding must not be used for circuits carrying 
more than 1,320 watts of energy; therefore, its use is re¬ 
stricted to small motors. 

The two most widely used systems in wiring for mo¬ 
tors are open work on knobs, and rigid conduit. Open 
w r ork is much cheaper and is much more extensively 
used. It serves the purpose very well if the motor is 
near the wall and if the wires on the side wall will not 
be subjected to mechanical injury. Rigid conduit is su¬ 
perior to all other systems of wiring for motors, because 
it protects the wires from mechanical injury and carries 
them in a compact form. Where motors are located 
away from the side walls or partitions, rigid conduit 
forms an excellent protection for the wires across the 
floor. 

Some Code Requirements. —Some of the Code re¬ 
quirements for installing and wiring motors will be dis¬ 
cussed, but the student should become familiar with this 
subject in the Code before undertaking any practical 
work. ‘‘Motors operating at a potential of 550 volts or 
less must be thoroughly insulated from the ground when¬ 
ever feasible.” “Wooden base frames and wooden floors 
are considered as sufficient insulation if they are kept 
filled to prevent the absorption of moisture and are kept 
clean and dry.” “Motors when combined with ceiling 
fans must be hung from insulated hooks, or else there 

380 


WIRING FOR MOTORS 


181 


must be an insulator interposed between the motor and 
its support.” 

“Small motors may be grouped under the protection 
of a single set of fuses, provided the rated capacity of 
the fuse does not exceed 6 amperes.” “Motors of this 
class seldom require a starting resistance and are thrown 
across the line when the switch is closed.” With motors 
of Jth horse power or less, on circuits where the voltage 
does not exceed 300, single-pole switches may be used. 

Larger motors, varying in size from one-fourth to 
one-half horse power and upward must have a special 
branch circuit run from the mains, which wires must 
have a current-carrying capacity at least 25 per cent 
greater than the motor is rated to take, as motors, when 
starting, take momentarily more than their rated current. 
The motor, and resistance box, if any is used, must be 
protected by a cut-out and controlled by a switch which 
plainly indicates whether it is “on” or “off.” The fuses 
used may be of the plug type if the current carried is 
not more than 30 amperes. If the current carried ex¬ 
ceeds 30 amperes, the cartridge fuse must be employed. 

Knife switches are used in controlling the larger mo¬ 
tors for three reasons: First, all the wires leading to 
the motor may be opened by the switch; second, the 
switch indicates whether or not the current is passing to 
the motor; third, knife switches may be obtained for 
either large or small current-carrying capacities. 

“The switch and rheostat must be located within sight 
of the motor.” This enables the operator to see the 
performance of the motor while manipulating the switch 
or rheostat. 

Direct Current Motors. —Direct current motors are 
designed to work on a constant potential; that is, the 
same potential that is ordinarily used for lights. They 
are built to be connected across no, 220 and 550 volts 
and are usually wired with a resistance to be cut in the 
circuit, to limit the current when starting. The no- and 


PRACTICAL ELECTRIC WIRING 


182 

220-volt motors are used extensively; the 550-volt mo¬ 
tors are seldom used industrially, because a circuit 
with such a high potential is seldom permitted in build- 
ings. 

Types. —There are three different types of direct 
current motors in commercial use, namely, shunt, se¬ 
ries, and compound motors. Each has its field and ar¬ 



mature windings connected differently and is suitable for 
a particular kind of service. 

Shunt Motor .—The shunt motor has its field and arma¬ 
ture connected in parallel, which fact causes it to give 
a speed that is practically constant under all variations 
in load. The starting torque or pull of the shunt motor 
is comparatively weak and for this reason the load is 
usually connected to the motor after it is up to speed. 
Friction clutches of various types are commonly used 
for connecting motors to their load. The shunt motor is 
used for running lathes and other machinery where a 
practically constant speed is desired. The wiring for such 




























WIRING FOR MOTORS 183 

a motor, with the wires carried on split knobs, is shown 
in Fig. 118. 

Mounting Switch and Starting Box .—The cut-out 
switch and starting box shown in the figure should be 
at least 4^ feet above the floor. The starting box, if 
mounted over combustible material, must be separated 
therefrom by a slab of soapstone, marble or slate, at 
least half an inch thick, and somewhat larger than the 
starting box in length and breadth. Slate is commonly 
used. The slate must be secured in its position inde¬ 
pendently of the rheostat supports. The following plan 
should be followed in mounting a starting box or other 
rheostat. Holes are drilled under the feet of the box 
through which bolts are to be passed that secure the box 
in place. These holes should be drilled with a larger 
drill for a short distance so that when the bolts are put 
into place, the heads are countersunk at least ■£ inch be¬ 
low the surface of the back of the slab. The drill holes 
over the bolt heads should then be filled with sealing 
wax flush with the back surface of the slab. Other holes 
are then,drilled for the wood screws and the slab is put 
into place. 

Wiring .—In connecting the wires to the starting box 
and motor, as shown in Fig. 118, one wire from the switch 
connects to the armature and field connections joined. 
The other line wire connects to the binding post, at the 
box marked L; the binding post marked A on the box 
is connected to the armature of the motor and the ter¬ 
minal marked F on the box is connected to the field 
of the motor. The terminals of the motor may or may 
not be marked with the letters F and A, but it is usually 
an easy task to trace the wires. The terminals that con¬ 
nect to the brushes on the commutator are the armature 
connections and the terminals that connect to the field 
coils are, of course, the field connections. 

If the motor has a potential of less than 300 volts, the 
wires must be kept 2 .\ inches apart and half an inch from 


184 


PRACTICAL ELECTRIC WIRING 


the surface wired over. Where this distance between 
wires and from the surface wired over cannot be main¬ 
tained, each wire must be protected by a separate casing, 
such as porcelain tubes or circular loom. Circular loom 
or some similar casing for the wires must be used at the 
motor and starting box. The casing should cover each 
wire in one continuous piece from the last knob to the 
connection on the motor or starting box. 

Starting .—The object of the starting box is to limit 



the current taken by the motor when starting, and the 
handle which cuts out resistance should be brought over 
slowly. To start a motor, the knife switch is closed and 
the handle of the rheostat is carried over the contacts 
gradually until it has reached die last contact, at which 
time the motor should be running at almost full speed. 
The time required to perform this operation differs for 
different-sized motors, or for motors with different start¬ 
ing loads. However, for small motors, five to ten sec¬ 
onds are required for proper starting. 

Reversing a Shunt Motor .—After a motor is installed, 
it often runs in the wrong direction The direction of 





























WIRING FOR MOTORS 


185 

rotation of a direct current motor may be reversed by re¬ 
versing the direction of the current in either the arma¬ 
ture or the field coils. Having a motor with four binding 
posts, as shown in Fig. 119, the direction of rotation may 
be reversed by interchanging the connections of the wires 
c and d, to the binding posts e and f. 

If the motor has only three places for connections it 



is then necessary to reverse either the field or the arma¬ 
ture leads within the motor. One of these three ter¬ 
minals has two wires connected under it, one from the 
armature and one from the field, and is usually marked 

L. 

Often it is desirable to reverse the direction of rota¬ 
tion with a reversing switch. This may be done, as 
shown in Fig. 120. 

A two-pole reversing switch may be used instead of a 









































PRACTICAL ELECTRIC WIRING 


186 

three-pole switch, but the motor is much less liable to 
injury with the latter because it opens the circuit to both 
the field and the armature circuit. 

Controlling Speed of Motors .—Where it is desirable 
to vary the speed of the motor, this may be done by plac¬ 
ing a variable resistance in either the field or the arma¬ 
ture circuit. To speed up the motor, open the wire at 
d and connect in series a field rheostat. Turning the 
handle of the rheostat so as to put more resistance in 
the circuit will increase the motor’s speed, and turning 
the handle so as to cut out resistance will slow the motor 
down. Too much resistance must not be placed in the 
field circuit, as it may cause the motor to spark at the 
brushes and burn out under a heavy load. To slow down 
the motor, open the armature wire at e and place a 
rheostat in series. Increasing the resistance in the cir¬ 
cuit will decrease the speed of the motor, and decreasing 
the resistance will increase the speed of the motor. By 
this method, the speed may be varied from a standstill 
to the normal speed of the motor. Other methods of 
speed control are used which embody this same prin¬ 
ciple ; that is, by varying the voltage applied to the 
brushes. 

The Series Motor .—The series motor, as the name • 
implies, has its field and armature windings connected 
in series. It has a strong starting torque and a variable 
speed; there is practically no limit to the speed of a 
series motor, when thrown across the line without any 
load. Some means must be provided to control the speed. 
This may be done by using a controller such as is em¬ 
ployed on street cars, or by employing a load which in¬ 
creases as the speed rises, such as is found on a fan 
motor. . 

Wiring .—The wiring for a series motor with a con¬ 
troller is shown in Fig. 121. 

The wiring for a series motor with a controller and 
reversing switch is shown in Fig. 122. 


WIRING FOR MOTORS 


187 


Compound Motors .—Compound motors are used where 
a motor is required that will start under a heavy load 
and run at practically constant speed. They are com¬ 
monly used for elevators, hoists, etc. The compound 
motor has a field coil of coarse wire connected in series 
with the armature and a shunt winding in parallel with 
the armature The series field is here arranged to aid 
the shunt field and thus give a, large starting torque. 




When full speed is attained the series field is cut out, 
and the motor thereafter runs as a shunt motor at a con¬ 
stant speed. Were the series field not cut out, the motor 
would vary in speed under different loads, as does a 
series motor. This variation of speed would, of course, 
be prohibited for an elevator. 

Wiring .—The wiring for a compound motor, with a 
starting box, is shown in Fig. 123. The wiring for a 
compound motor with a starting box and reserving switch 
is shown in Fig. 124. 

















































PRACTICAL ELECTRIC WIRING 


Controlling Speed .—The speed of a compound motor 
may be varied by placing resistance in either or both the 
field and armature circuits. Placing a variable resist¬ 
ance in the wire b, Fig. 123, and in the wire c, Fig. 



124, will increase the speed of the motors; while plac¬ 
ing a variable resistance in the wire d, Fig. 123, and 
in the wire e, Fig. 124, will decrease the speed of the 
motors. By combining these two resistances, a wide 
range of speed control may be obtained. 

Alternating Current Motors.—The wiring for alter¬ 
nating current motors may be installed with any of the 






















WIRING FOR MOTORS 


189 


systems used for direct current motors. The same rules 
apply, except as to the size of branch circuits or leads 
to the motor. The wires for this purpose must be de¬ 
signed to carry a current at least 25 per cent greater 
than that for which the motor is rated. Also, “where 
wires under this rule would be overfused in order to 



provide for the starting current, as in case of many 
alternating current motors, the wires must be of such 
size as to be properly protected by these larger fuses.” 

Classes— The motors used on alternating current 
circuits may be divided into two classes, namely, single 
phase and polyphase. In the single-phase class, two 
kinds are obtainable—series and induction motors. Un¬ 
der the polyphase class come induction and synchronous 
motors. Single-phase motors require only two wires 
from the mains to the cut-out and switch. The number 


















































PRACTICAL ELECTRIC WIRING 


190 

required from the switch to the motor will depend on the 
method of starting the motor. 

Series Motor .—The series motor used on alternating 
current is similar to the direct current series motor, 
shown in Fig. 121. * The motor has a commutator and 
brushes like those of the D. C. motor and the field and 
armature are connected in series, though it is a little 
smaller, for the same rating than the direct current, be¬ 
cause less iron is used in its construction. In starting, 
small motors of this type are thrown directly across the 
line; while the larger motors are started with an external 
resistance or reactance connected in one wire leading to 
the motor as the starting box is connected in Fig. 121. 

The use of the series motor is restricted almost entirely 
to fans, dental engines and similar work, and on a larger 
scale to street railways or electric locomotives. 

Induction Motor .—The induction motor has its field 
and armature windings separate; that is, they are entirely 
insulated from each other. The current from the line 
is usually introduced into the field or stationary member 
and the current is induced in the armature or rotating 
member. The armature may be a wound or a squirrel- 
cage type of armature but no commutator is required for 
either, as the rotating effort is due to a combination of 
transformer and motor action between the two windings. 

Starting .—Small single-phase motors and some 
larger ones are designed to be inherently self-starting. 
The wiring for such a motor would naturally only in¬ 
clude carrying the two wires from the mains through 
a cut-out and switch to the motor. 

The larger motors require such large currents for 
starting when thrown directly across the line that some 
method of limiting the initial rush of current to the motor 
must be used. Resistance or reactance may be placed in 
the circuit leading to the motor, though the most satis¬ 
factory plan is to use a combination of the two which 
is found in some of the standard starters. These starters 


WIRING FOR MOTORS 


191 


usually have a double-throw switch, which is thrown 
into one position for starting and into another position 
for running. Such a starter for a single-phase induc- 



Figure 125. 


tion motor, with a two-phase or with a single-phase and 
an auxiliary winding, is shown in Fig. 125. 

The largest motors used on single-phase have their 



windings separated into three parts as if they were to 
be used on three-phase. Fig. 126 shows the connections 













































192 


PRACTICAL ELECTRIC WIRING 


for starter and single-phase induction motors, with a 
three-phase winding. 

Reversing .—To change the direction of the rotation 
of this motor, it is only necessary to reverse the wires 
a and b at the starting box, or at the motor. 

The three windings of a motor are usually connected in 
what is called a “delta” for running, as shown in Fig. 




127B, but where this connection is made permanently in 
the motor, the same connection must also be used for 
starting. If these windings can be connected in “star” 
for starting, as shown in Fig. 127A, the motor will take 
a much smaller starting current. 

A starting box which uses both resistance and react¬ 
ance and connects the windings in “star” when starting 
and in “delta” when running, is shown in Fig. 128. It is 
necessary in wiring for this box and motor to carry the 
two wires from each winding of the motor to the start¬ 
ing box, as shown in Fig. 128. , 

Reversing .—The direction of rotation of this motor 
may be reversed by reversing the position of the wires 
on the starter that comes from the resistance and re- 
















WIRING FOR MOTORS 


193 


actance, as shown at R and L in the figure. The external 
connections for Fig. 128 are shown in Fig. 129. 

In installing induction motors with starters, the wire- 



man should be guided by the diagrams and instructions 
provided by the manufacturer. 

Starting Polyphase Induction Motors. —Polyphase, or 


































































194 


PRACTICAL ELECTRIC WIRING 


two- and three-phase, induction motors are inherently 
self-starting; and small motors of this type may be 
thrown directly across the line. To limit the current 
taken by large motors of this type in starting, one of 
two types of starters is generally used. One type em¬ 
ploys a resistance unit for each phase, which is placed in 

4 

L / ne 



series with the phases when starting and is cut out after 
the motor reaches full speed. A more expensive, but 
much more satisfactory, starter employs an auto-trans¬ 
former for each phase. Taps are taken out from the 
transformer which make it possible to select a voltage 
for starting that is suitable for that particular motor. 
With a resistance starter, some form of double-throw 
switch is arranged to connect resistance in series with 










































WIRING FOR MOTORS 


195 


each phase for starting and to connect the motor directly 
across the line for running. 

The connections of a self-contained auto-starter for a 
two-phase induction motor are shown in Fig. 130. 

The auto-starter, or compensator shown in Fig. 130, 



gives the arrangement of all the internal connections. 
In practice it is only necessary to connect the marked 
terminals to the four wires from the line and the other 

four terminals to the motor. 

Reversing .—To reverse the diiection of rotation of a 
two-phase motor, reverse the wires of one phase. If 
the circuit used should be a 3-wi^e, 2-phase, instead of a 
4-wire, 2-phase, the direction of rotation may be. re¬ 
versed by reversing the position of the two smaller wires. 









































196 


PRACTICAL ELECTRIC WIRING 


On such a circuit the wire that is common to both 
phases must be one and one-half times larger than either 
of the other two wires. This wire remains as connected 
and the other two are reversed. 

Three-phase induction motors are started by an auto¬ 
starter or compensator similar to the one used for two- 


Lin e 



phase motors. Fig. 131 shows the connections for such 
a starter. 

This starter is self-contained. To install it, it is only 
necessary to connect to the marked terminals the three 
wires from the motor. 

To reverse the direction of rotation of a three-phase 
motor, reverse the connections of any two wires. 

Three-phase induction motors are on the market which 
employ a wound stator and a wound rotor. This wound 
rotor is sometimes used for starting by taking taps from 
the winding and connecting them to a resistance which 
may be either internal or external to the motor. This 
resistance is placed in circuit with the winding for start- 
































WIRING FOR MOTORS 


197 


mg and is short-circuited while running. The resistance 
may be cut in and out of circuit by a lever on the ma¬ 
chine or by an external switch. Fig. 132 shows the con¬ 
nections for such a motor. 

Where the resistance used is external to the motor, 
the speed of the motor is sometimes regulated by placing 
part of the resistance in the rotor circuit. 

Synchronous Motors .—Synchronous motors of the 



larger size are sometimes used on alternating current 
circuits. They run at the same speed, pole for pole, as 
the alternator furnishing the current and have the ad¬ 
vantage that they improve the power factor of the line. 
They may be used on single-phase, two-phase or three- 
phase circuits, though in practice they are seldom used 
except in three-phase circuits. The synchronous motor 
requires a direct current source of power to excite one 
of the windings, which is called the field of the motor. 
The field may be the stationary or the revolving member. 
Fig. 133 shows a three-phase synchronous motor with a 
revolving field. 













198 


PRACTICAL ELECTRIC WIRING 


QUESTIONS. 

1. What wiring systems may be used in wiring for 

motors? 

2. What two systems are most widely used in wiring for 

motors? Which is the better, and why? 

3. What are the Code requirements in regard to insulating 

motors from the ground? 

4. Under what conditions may single-pole switches be used 

for motors? 

5. What sized wire is required for motors? 

6. What is the largest current w r hich plug fuses are per¬ 

mitted to carry? 

7. What kind of switches are usually employed in con¬ 

trolling the larger motors? Why? 

8. Where must the switch and rheostat be placed in respect 

to the motor? 

* 

9. Explain the connection of the field and armature wind¬ 

ings of a shunt motor. 

10. For what purpose are shunt motors used in practice? 

11. How high above the floor should a motor’s switch and 

starting box be placed? 

12. Explain in detail a method of mounting a starting box 

or rheostat. 

13. In wiring for motors with open work, where is circular 

loom required on the wires? 

14. Explain the method of starting a direct current motor* 

15. How may the direction of rotation of a shunt motor be 

reversed? 

16. How may the speed of a shunt motor be increased? Be 

decreased? 

17. Explain the connection of the field and armature wind¬ 

ings in a series motor. 

18. For what purpose are series motors used in practice? 

19. How may the direction of rotation of a series motor 

be reversed? 

20. How are the field coils and the armature of a compound 

motor connected? 

21. For what purposes are compound motors used in prac¬ 

tice ? 


WIRING FOR MOTORS 


199 


22. How may the direction of rotation of a compound motor 

be reversed? 

23. What types of motors are used on alternating current 

circuits ? 

24. For what purposes are series A. C. motors used in 

practice? 

25. Explain the different methods of starting single-phase 

induction motors. 

26. Explain the method of reversing the direction of rota¬ 

tion of a three-phase motor used on single-phase. 

27. Show by diagram the windings of a three-phase motor 

connected in “delta.” In “star.” 

28. What forms of starters are employed for starting large 

polyphase induction motors ? 

29. How may the direction of rotation of a 2-phase, 4-wire 

induction motor be reversed? A 2-phase, 3-wire? 

30. How may the direction of rotation of a 3-phase motor 
* . be reversed? 

31. What method is sometimes employed for regulating the 

speed of a 3-phase induction motor? 


/ 


Exercises for Practice. 




200 














































































































































201 

































23ranch 14//res 




















CHAPTER XI 


TELEPHONES 

Important Requirements —The wiring for tele¬ 
phones, like other low voltage wiring, is covered by only 
a few Code requirements. The reason for these require¬ 
ments is chiefly the possibility of the telephone wires' 
coming into contact with heat, light or power wires. The 
requirements for telephones in the Code are given under 
signaling systems, and as a convenience to the reader the 
rules that apply especially to telephones will be given. 

Rule No. 85; Section A. 

(a) Outside wires should be run in underground ducts or 
strung on poles, and kept off the roofs of buildings, except 
by special permission, and must not be placed on the same 
cross-arm with electric light or power wires. They should 
not occupy the same duct, man-hole or hand-hole of a con¬ 
duit system with electric light or power wires. Single man¬ 
holes, or hand-holes separated into sections by means of 
partitions of brick or tile will be considered as conforming 
with the above rule. 

When the entire circuit from central station to build¬ 
ing is run in underground conduits the following rules do 
not apply. 

(b) When outside wires are run on the same pole with 
electric light or power wires, the distance between the two 
inside pins of each cross-arm must not be less than twenty- 
four inches. 

When the wires are carried in approved cables the next 
three sections, c, d, and e, do not apply. 

(c) When wires are attached to the outside walls of 
buildings, they must have an approved rubber insulating 

203 


204 


PRACTICAL ELECTRIC WIRING 


covering, and on frame buildings or frame portions of other 
buildings shall be supported on glass or porcelain insulators, 
or knobs. 

(d) The wires from last outside support to the cut-outs or 
protectors must be of copper, and must have an approved 
rubber insulation, and must be provided with drip loops 
immediately outside the building and at entrance. 

(e) Wires must enter building through non-combustible, 
non-absorptive, insulating bushings sloping upward from 
the outside; and both wires may enter through the same 
bushing if desired. 

Telephone Protectors. —Installations where the cur¬ 
rent-carrying parts of the apparatus are not capable of 
carrying indefinitely a current of io amperes: 

The installation must be provided with an approved 
protective device located as near as possible to the en¬ 
trance of the wires to the building. The protector must 
not be placed in the immediate vicinity of easily ignitible 
stuff, or where it is exposed to inflammable gases or dust 
or flyings of combustible materials. 

Wires from entrance to building to protector must 
be supported on porcelain insulators, so that they will not 
come into contact with anything except their designed 
supports. 

The ground wire of the protective device shall be run 
in accordance with the following requirements: 

1. It shall be of copper and not smaller than No. 18 
B. & S. gauge. 

2. It must have an insulating covering approved for 
voltages from o to 600, except that the preservative com¬ 
pound may be omitted. 

3. It must run in as straight a line as possible to a 
good permanent ground. This may be obtained by con¬ 
necting to a water or gas pipe connected to the street 
mains or to a ground rod or pipe driven into permanently 
damp earth. When connections are made to pipes, pref¬ 
erence shall be given to water pipes. If attachment is 


TELEPHONES 


205 


made to a gas pipe, the connection in all cases must be 
made between the meter and the street mains. In every 
case the connection shall be made as near as possible to 
the earth. 

When the ground wire is attached to a water pipe or 
a gas pipe, it may be connected by means of an approved 
ground clamp fastened to a thoroughly clean portion of 
said pipe, or the pipe may be thoroughly cleaned and 
tinned with resin flux solder, and the ground wire then 
be wrapped tightly around the pipe and thoroughly 
soldered to it. 

When the ground wire is attached to a ground rod 
driven into the earth, the ground wire shall be soldered 
to the rod in a similar manner. 

Steam or hot water pipes must not be used for a pro¬ 
tector ground. The protector, referred to in the pre¬ 
ceding rules, consists of a fuse, a lightning arrester and 
a heat coil. Though a lightning arrester is usually pro¬ 
vided on the telephone, this is not considered as suf¬ 
ficient protection. A standard arrester and fuses should 
be added to the circuit, as the protector and heat coils 
should also be inserted, where the circuit, normally closed, 
through the magnet windings cannot indefinitely carry 
a current of at least five amperes. The fuses must be 
so placed as to protect the arrester and the heat coils. 

Telephone Wiring. —The wires from the fuses and 
arrester may be run concealed or open. When it is prac¬ 
tical the wires should be concealed and this is very de¬ 
sirable if there are a number of wires. The wires may 
be grouped into a cable and passed in partitions or be¬ 
tween floors; however, a more substantial and satisfac¬ 
tory plan is to run them in a conduit raceway. Such con¬ 
duits should be installed during the construction of the 
building. 

Open Wiring .—Open wiring is usually done with a 
twisted pair held in place with nails having insulated 
heads. Such wires are usually passed around window 


20 6 


PRACTICAL ELECTRIC WIRING 


facings, door jambs, and along baseboards to make them 
less conspicuous. The wires should be insulated by a 
substantial covering from each other and from any non¬ 
conducting surfaces wired over. Where a space of at 
least two inches cannot be maintained between telephone 
wires and electric light and power wires, or iron pipes, 
steel girders, etc., an extra insulation such as a porcelain 
tube should be placed over the wires. 

Caution.—Telephone wires should never be placed 
in the same duct with or run near light or power wires, 



not only because of the possibility of the wires’ coming in 
contact with each other, but because parallel power wires 
often produce by induction objectionable noises in the 
telephone receivers. 

Kinds of Telephone Systems. —Telephone wiring 
may be roughly divided into two classes; namely, that 
done by the owner of a building and that done by the 
telephone company. Under the former should come the 
installing and wiring for any telephones that may be 
required in the establishment, such as private or inter¬ 
communicating systems. Under the latter should come 
the installing and wiring for any telephones placed on the 








































TELEPHONES 


207 


premises by the local telephone company, including ex¬ 
tensions and private branch exchanges. 

Two-party System .—Perhaps the simplest example of 



an interior telephone system is a battery system between 
two parties, as shown in Fig. 134. 

As shown in the figure, signaling is done with a bat- 




























































































































208 


PRACTICAL ELECTRIC WIRING 


tery, double contact push buttons and a vibrating bell. 
When the receivers are taken from the hooks the cir¬ 
cuit is closed through both transmitters, receivers and 



aid each other when the talking circuit is made. This 
type of telephone when wired with No. 18 wire is very 
satisfactory for distances up to 5 00 feet. 


































































































TELEPHONES 


209 


Kitchen Annunciator System .—Often it is desirable to 
install a telephone annunciator system, instead of an ex¬ 
isting return call annunciator system, in a private resi- 



Figure 138. 


dence or hotel. The existing wiring may be used for 
this system by installing telephones instead of the bells 
and buttons in the rooms and replacing the old annuncia¬ 
tor with one employing a telephone. Fig. 135 shows this 





210 


PRACTICAL ELECTRIC WIRING 


plan applied to a kitchen annunciator telephone system. 
With this arrangement the room can call the annunciator 
but the servant cannot call the room. 

Hotel Annunciator System .—The same plan is applied 
on a larger scale to hotel telephone annunciators. The 
connections of such a system using three-room telephones 
and employing the existing wiring for a return call an¬ 
nunciator is shown in Fig. 136. Each room telephone is 

ROOM 'PHONES ENTRANCE JANITOR 



connected to one individual wire that runs to the an¬ 
nunciator and to the two common return wires. 

The diagram for a similar system employing two-room 
telephones is shown in Fig. 137. An illustration of a 
telephone annunciator to be used with this diagram is 
shown in Fig. 138. The operation of the system is as 
follows: 

To call the office from a room, press the button on the 
room set. This indicates on the annunciator the point 
from which the call is made. The attendant at the annun¬ 
ciator inserts a plug in the corresponding room number 
on the telephone board and answers call by pushing but¬ 
ton located on the annunciator. LTpon the room bell’s 
ringing, the person in the room takes the receiver off the 
hook and proceeds with the conversation. When the 
plug is in position on the board, no other room can hear 































































TELEPHONES 


211 


the conversation, but should a call come in from any 
room it would be indicated on the annunciator. 

To call a room, insert a plug in the hole correspond¬ 
ing to the point desired and press the push on the an¬ 
nunciator. 



Figure 140. 


This can be made intercommunicating by using an ex¬ 
tra set of plugs and an extra battery. When used for 
intercommunicating it does not interfere with the calling 
or talking on any other portion of the system. No con¬ 
versation can be heard outside of those in communica¬ 
tion. 














212 


PRACTICAL ELECTRIC WIRING 


Six to eight cells of battery are usually ample for an 
ordinary house or hotel annunciator. This system is 
arranged for 2 leading wires and i battery wire; in other 
words, for a hotel of ioo rooms there would be 201 wires 
required. 

Apartment House System .—A type of telephone sys¬ 
tem designed to take the place of speaking tubes in apart¬ 
ment houses is shown in Fig. 139. This system permits 



Figure 141. 

communication between the entrance and the rooms and 
between the janitor and the rooms. One set of battery 
is employed for both ringing and talking circuits. 

Intercommunicating System .—Where it is desired to 
converse between the different parts of an establishment 
without using a common switch board, a type of tele¬ 
phone called intercommunicating is employed. This 
type of telephone employs some switching arrangement 
on each case by means of which the circuit to any tele¬ 
phone in the system may be closed for signaling and con¬ 
versation. Fig. 140 shows the instrument and Fig. 141 
the wiring for three such telephones. 

Much time will be saved in the wiring if wires with 
different colored insulation are used for this class of 































































TELEPHONES 


213 


installation. For instance, it is a good plan to use red 
for the common return wire, blue for the talking battery 
wire, yellow for the telephone wire, and white for the 
switch wires to the telephones. An objection sometimes 
made to this system is that there may be cross-talk when 
more than one pair of telephones are being used. Such 
cross-talk will not occur on a full metallic system, as 
shown in Fig. 142. Four cells of battery connected as 



Figure 142. 


shown in the figure are usually sufficient to operate such 
a system. 

Standard Wall Sets .—Telephones for longer distance 
service including party lines, exchanges and long dis¬ 
tance communication, commonly employ a hand magneto 
generator and a polarized bell for ringing and an induc¬ 
tion coil to increase the magnitude of the talking current. 
Such a standard wall set with a list of important parts 
used in its construction is shown in Fig. 143. 

The usual internal wiring for such a standard wall set, 
when connected from an exchange or on a party line, 
is shown in Fig. 144. 

As shown in the diagram, when the receiver is on the 














































































214 


PRACTICAL ELECTRIC WIRING 



hook the external circuit is closed through the bells, the 
generator being open-circuited by a switch operated from 
the crank. When the crank is turned, a switch is closed 


Figure 143. 

A—Transmitter mouthpiece; B—Transmitter back shell; C—Enam¬ 
eled transmitter arm complete; E—Ringer coil; F—Ringer magnet; 
G—Line binding posts complete with plates; H—Carbon disc for light¬ 
ning arrester; I—Induction coil complete; J—Hook lever; K—Receiver 
shell or body; L—Receiver cap, M—Receiver cords; N—Magnet for 
generator; O—Generator shunt springs complete; P—Wire terminal; 
Q—Dry batteries; R—Transmitter cord; S—Springs for hook switch; 
T—Large gear wheel; U—Ground spring complete with binding post; 
V—Small gear wheel for generator; W—Writing shelf with bracket; 
X—Front door for cabinet; Y—Diagram card; Z—Complete telephone 
cabinet. 

through the generator, which places the generator in 
parallel with the home bell and the distant bell for signal¬ 
ing purposes. Removing the receiver from the hook 



























TELEPHONES 


215 


allows the hook switch to rise, placing the receiver on 
the line in series with the secondary of the induction coil. 
At the same time the local circuit for talking purposes 
is closed through the battery transmitter and primary of 
the induction coil. Use of the induction coil has the 
advantage of removing the transmitter from the line cir¬ 



cuit where a given change in resistance would produce 
a small alteration of current, and of placing it in a local 
circuit where the same amount of variation in resistance 
will cause a large alteration of current. Through the 
inductive action of the coil this effect is transferred in 
its magnified form to the secondary circuit which is con¬ 
nected in the main line. At the same time it transforms 
the talking current from a low voltage and large current 





































2l6 


PRACTICAL ELECTRIC WIRING 


to a higher voltage and smaller current, which can more 
readily be transmitted to a distant receiver. 

Such telephones, when connected upon individual lines 
from an exchange, usually employ two wires from the 
exchange to the telephone. This is generally known as 
a full metallic circuit. They may be connected by using 
one wire and a ground return, but this is not considered 


Line wires 


oo 

£ xtens/or? 


Figure 145. 

good practice as other currents flowing through the earth 
may cause a noisy system. 

Extension Bells .—Extension bells are sometimes con¬ 
nected to telephones for signaling. These are for calling 
only and have no telephones attached thereto. The wir¬ 
ing for such a bell on a bridging phone consists in con¬ 
necting the two wires from the extension bell to the tele¬ 
phone line wires, either on the terminal block of the 
telephone itself or to another part of the line, as shown in 

Fig- 145- 

For a series telephone line, where two or more tele¬ 
phones are connected in series, an extension bell may be 
placed in circuit by connecting it in series with the gen¬ 
erator and bell on such a wall set, as shown in Fig. 146. 



T^e/e/ohone. 




















TELEPHONES 


217 


For either the bridging or series telephone the exten¬ 
sion bell used should be of the same type and have the 
same resistance as the telephone bell. 

Party Lines .—Where two or more telephones are con- 



Figure 146. 





































































2l8 


PRACTICAL ELECTRIC WIRING 


nected to the same wire or pair of wires either in series 
or in multiple, it is called a party line. The internal wir¬ 
ing for a telephone employed on a party line is shown 



Figure 147. Bridging Metallic Line 


in Fig. 144 for the bridging line and No. 146 for the 
series line. When two or more telephones are connected 
together in series, as shown in Fig. 149, the circuit is 
designated as a series metallic line. Instruments used for 



Figure 148. Bridging Grounded Line 

this purpose must be alike, and the bells and magnetos 
must be of suitable resistance for series operation. 

When a number of telephones are connected together 
in multiple, as shown in Fig. 147, the circuit is desig¬ 
nated a bridging metallic line. Here also, all instruments 


















































TELEPHONES 


219 


must be alike and the bells and magnetos must be of 
similar resistance for multiple operation. The bells 
should have a resistance of from 1,000 to 1,200 ohms 
and the magnetos, about 350 ohms. In addition to the 



metallic circuit, series and bridging lines shown in Figs. 
149 and 147, the same result may be accomplished with 
grounded returns as shown in Figs. 150 and 148. 

Of the four different connections the series grounded 



and the bridging grounded are the cheapest to install, 
though the number of telephones that will give satisfac¬ 
tion on such a circuit is usually limited to from four to 
six. With a series metallic line a few more telephones 


























































































































220 


Figure 151. 








































































































TELEPHONES 


221 


may be placed in circuit but the number is kept low be¬ 
cause of the high resistance of the telephone bells. The 
bells of the telephone in use are disconnected from the 
talking circuit when the receiver is removed from the 
hook but all the other telephone bells are left connected 
in the talking circuit. 

The bridging metallic line is the most satisfactory of 
all the party lines in use. The bells possess a high re¬ 
sistance and reactance which cause them to use a very 
small amount of the talking current that is passing on the 
line wires. 

Central Energy System .—The most widely used tele¬ 
phone system for exchange purposes in all large cities 
is the central energy system. With this system, instead 
of having a battery and a magneto in each subscriber’s 
telephone, the current for both talking and ringing pur¬ 
poses is supplied from the exchange. An alternating 
current of 75 volts and 15 cycles is furnished from a 
generator as the ringing current for all the telephones. A 
24-volt storage battery serves the double purpose of sup¬ 
plying the talking current for all the telephones and of 
supplying the current for signaling from the subscriber’s 
telephone to the central exchange. When the subscriber 
takes the receiver from the hook, he thereby closes a 
circuit from the battery through a relay, which in turn 
closes another circuit from the battery to a small lamp 
on the board, causing it to light and indicate the number 
that is calling. The connection of the Hayes central en- 
ergy system for conversation between the two subscrib¬ 
ers’ telephones is shown in Fig. 151. 

Though other central energy systems are in use, the 
general scheme for connecting the battery and the pri¬ 
vate telephones is very similar to the one here shown. 


222 


PRACTICAL ELECTRIC WIRING 


QUESTIONS. 

1. May telephone wires be carried in the same duct with 

light or power wires? 

2. How may telephone wires be run on the outside walls 

of buildings? 

3. What kind of wire must be used from the last outside 

support to the cut-out or protectors? 

4. Describe the method of entering the building w T ith the 

wires. 

5. Where should the protective device be located? 

6. State the requirements for the ground wire, to be run 

from the protector. 

7. How should the ground wire be fastened to the ground 

pipe? 

8. Of what does the protector consist? 

9. How may wires be carried, concealed, from the pro¬ 

tector to the telephone? 

10. Describe the usual method of carrying the wires in open 

work. 

11. How should the wires be insulated from power wires, 

iron pipes, etc. ? 

12. Why should telephone wires never be placed in the 

same duct or near light or power wires? 

13. Into what two classes may telephone wiring be divided? 

14. Sketch a battery telephone connection between two 

parties. 

15. Draw a diagram of wiring for a kitchen annunciator 

system and explain its operation. 

16. Sketch a similar system used for hotels. 

17. Explain the operation of a standard hotel annunciator 

system. 

18. Sketch a battery system for an apartment house. 

19. What is an intercommunicating system? 

20. Sketch the wiring plan for three intercommunicating 

telephones. 

21. What are some of the most important parts of a stan¬ 

dard wall set? 

22. Sketch the internal wiring plan of a standard wall set 

for a bridging system. 


TELEPHONES 


223 


23. What is the object of the induction coil? 

24. What is meant by a full metallic circuit? 

25. Sketch the wiring plan for an extension bell connected 

to a bridging telephone. 

26. Sketch the internal wiring plan of a standard wall set 

for a series system. 

27. What is a party line? 

28. Sketch three telephones connected 

(a) On a bridging metallic system, 

(b) Bridging grounded system, 

(c) Series metallic system, 

(d) Series grounded system. 

29. Which of the four different systems is the most satis¬ 

factory ? 

30. Describe the operation of a central energy system. 

31. Sketch the wiring plan for a conversation between two 

subscribers on a central energy system. 






APPENDIX. 


WIRING TABLES 

CONDUCTIVITIES. 

At o° C. At ioo° C. 

Metals. At 32 0 F. At 212 0 F. 

Silver, hard. 100. 71.56 

Copper, hard.. 99-95 70.27 

Gold, hard. 77.96 55-90 

Zinc, pressed. 29.02 20.67 

Cadmium. 23.72 16.77 

Platinum, soft. 18.00 

Iron, soft. 16.80 

Tin. 12.36 8.67 

Lead. 8.32 5.86 

Arsenic.. 4.76 3.33 

Antimony. 4.62 3.26 

Mercury, pure. 1.60 

Bismuth. 1.245 o. 878 


CONDUCTORS AND INSULATORS IN ORDER 
OF THEIR VALUE. 

Conductors. Insulators (Non-conductors). 

All metals Dry air Ebonite 

Well-burned charcoal Shellac Gutta-percha 

Plumbago Paraffin India-rubber 

Acid solutions Amber Silk 

Saline solutions Resins Dry paper - 

Metallic ores Sulphur Parchment 

Animal fluids Wax Dry leather 

Living vegetable substances Jet Porcelain 

Moist earth Glass Oils 

Water Mica 

According to Culley the resistance of distilled water is 6,754 
million times as great as that of copper. 

225 















226 


APPENDIX 


\ 


MELTING POINT AND RELATIVE ELECTRICAL CONDUC 
TIVITY OF DIFFERENT METALS AND ALLOYS. 


Metals. 

Pure silver. 

Pure copper. 

Refined and crystallized copper . 
Telegraphic silicious bronze. . . . 
Alloy of copper and silver (50%) 

Pure gold. 

Silicide of copper, 4% Si. 

Silicide of copper, 12% Si. 

Pure aluminum. 

Tin with 12% of sodium. 

Telephonic silicious bronze. 

Copper with 10% of lead_:. .. 

Pure zinc.. 

Telephonic phosphor-bronze 

Silicious brass, 25% zinc., 

Brass with 35% zinc. 

Phosphor tin. 

Alloy of gold and silver (50%).. , 

Swedish iron.. 

Pure Banca Tin.. 

Antimonial copper. 

Aluminum bronze (10%).. 

Siemens steel. 

Pure platinum. 

Copper with 10% of nickel. 

Cadmium Amalgam (15%). 

Dronier mercurial bronze. 

Arsenical copper (10%). 

Pure lead. 

Bronze with 20% of tin. 

Pure nickel.. 

Phosphor-bronze, 10% tin. 

Phosphor-c®pper, 9% phos.. 

Antimony. 


Relative 

Conductivity. 

100 . 

100 . 

• 99-9 
98. 

. 86.65 

. 78. 

• 75 - 

• 54-7 
54-2 

. 46.9 

35 - 
30. 
29.9 
29. 
26.49 
. 21.5 

17.7 
16.12 

. , 16. 

1545 

12.7 

12.6 
12.' 

10.6 
10.6 
10.2 
10.14 

9.1 

8.88 

8.4 
7.89 

6.5 
4.9 
3-88 


Melting 
Point 0 F. 


1873 

2550 


2016 


Il6o 


773 


4000 

442 


4100 


630 

2800 





































APPENDIX 


227 


CURRENT REQUIRED TO FUSE WIRES OF COPPER, GERMAN 



SILVER AND 

IRON. 



Copper, 

German Silver, 

Iron, 


B. & S. Gauge. Amperes. 

Amperes. 

Amperes. 

10. . 

. 333 - 

169. 

IOI . 

II.. 


146. 

86. 

12. . 

• .. 235. 

120.7 

71.2 

13 -. 

. 200. 

102.6 

63 - 

14.. 


85.2 

50.2 

15.. 

. 139 - 

71.2 

42.1 

16.. 

. 117 • 

60. 

35:5 

17.. 

. 99 - 

50.4 

32.6 

18.. 

. 82.8 

42.5 

25-1 

19.. 

. 66.7 

34.2 

20.2 

20. . 

. 58-3 

29.9 

17.7 

21 . . 

. 49-3 

25-3 

14.9 

22 . . 

. 41.2 

21.1 

12.5 

23 - • 

. 34-5 

17.7 

10.9 

24. . 

. 28.9 

14.8 

8.76 

25 . • 

. 24.6 

12.6 

7.46 

26. . 

. 20.6 

10.6 

6.22 

27. . 

. 17-7 

9.1 

5-36 

28 . . 

.•. 147 

7-5 

4-45 

29. . 

. 12.5 

6.41 

3-79 

30 . . 


5.26 

3 -ii 

31 . • 

. 8.75 

4.49 

2.65 

32 . • 

. 7.26 

3-73 

2.2 

33 - • 

. 6.19 

3-18 

1.88 

34 - • 


2.64 

1-55 

35 - • 

4-37 

2.24 

i -33 

36. . 


1.86 

1.09 

37 - • 


1.58 

• 93 

38. • 


1. 3 i 

• 77 

39 . • 

. 2.20 

1 .13 

.67 

40.., 

. 1.86 

• 95 

.56 

































22 8 


APPENDIX 


TABLE SHOWING DIFFERENCE BETWEEN WIRE GAUGES 
IN DECIMAL PARTS OF AN INCH. 

W ashbum Old 



American Birming 

& Moen 

Trenton 


English 

No. 

No. of 

or Brown 

ham or 

Mfg. Co., 

Iron Co., 

New 

from 

of 

Wire Gauge 

& Sharpe 

Stubs 

W orces- 

Trenton, 

British 

Brass 

Wire 




ter, Mass 

N. J. 

Mfrs. List 


oooooo. 


• • • • 

.46 

• • . • 

• • • • 

• • • • 

oooooo 

ooooo. 


• • . • 

• 43 

• 45 

• . * • 


ooooo 

0000. 

.46 

• 454 

• 393 

• 4 

• 4 


0000 

ooo. 

.40964 

.425 

.362 

.36 

.372 


000 

00. 

.3648 

.38 

• 331 

• 33 

.348 


00 

o. 

•32495 

.34 

.307 

.305 

.324 


0 

i. 

.2893 

• 3 

.283 

.285 

• 3 


I 

2. 

.25763 

.284 

.263 

.265 

.276 


2 

3 . 

.22942 

.259 

.244 

.245 

.252 


3 

4 . 

.20431 

.238 

.225 

.225 

.232 


4 

5 . 

.18194 

.22 

. 207 

.205 

.212 


5 

6. 

.16202 

.203 

. 192 

.19 

. 192 


6 

7 . 

.14428 

.18 

.177 

.175 

. 176 


7 

8. 

.12849 

.165 

. 162 

. 16 

. 16 


8 

9 . 

•II 443 

. 148 

. 148 

.145 

.144 


9 

10. 

.10189 

.134 

.135 

.13 

. 128 


10 

ii . 

.090742 

. 12 

. 12 

.1175 

. 116 


II 

12. 

.080808 

. 109 

.105 

.105 

. 104 


12 

13 . 

.071961 

.095 

.092 

.0925 

.092 


13 

14 . 

.064084 

.083 

.08 

.08 

.08 

.083 

14 

15 . 

.057068 

.072 

.072 

.07 

.072 

.072 

15 

16. 

.05082 

.065 

.063 

.061 

.064 

.065 

l6 

17 . 

.045257 

.058 

.054 

.0525 

.056 

.058 

17 

l8. 

.040303 

.049 

.047 

.045 

.048 

.049 

18 

19 . 

.03589 

.042 

.041 

.039 

.04 

.04 

19 

20. 

.031961 

.035 

.035 

.034 

.036 

.035 

20 

21. 

.028462 

.032 

.032 

.03 

.032 

.0315 

21 

22. 

.025347 

.028 

.028 

.27 

.028 

.0295 

22 

23 . 

.022571, 

.025 

.025 

_ .024 

.024 

.027 

23 

24 . 

.0201 

.022 

.023 

.0215 

.022 

.025 

24 

25 . 

.0179 

.02 

.02 

.019 

.02 

.023 

25 

26. 

.01594 

.018 

.018 

.018 

.018 

.0205 

26 

27 . 

.014195 

.016 

.017 

.017 

.0164 

.01875 

27 

28. 

.012641 

.014 

.016 

.016 

.0148 

.01651 

28 

29 . 

.011257 

.013 

.015 

.015 

.0136 

.0155 

29 

30 . 

.010025 

.012 

.014 

.014 

.0124 

.01375 

30 

31 . 

.008928 

.01 

.0135 

.013 

.0116 

.01225 

31 

32 . 

.00795 

.009 

.013 

.012 

.0108 

.01125 

32 

33 . 

.00708 

.008 

.011 

.011 

.01 

.01025 

33 

34 . 

.006304 

.007 

.01 

.01 

.0092 

.0095 

34 

35 . 

.005614 

.005 

.0095 

.009 

.0084 

.009 

35 

36 . 

.005 

.004 

.009 

.008 

.0076 

.0075 

3 b 

37 . 

.004453 

• • . • 

.0085 

.00725 

.006S 

.0065 

37 

38 . 

.003965 

. . . • 

.008 

.0065 

.006 

.00575 

38 

39 . 

•003531 

.... 

.0075 

.00575 

.0052 

.005 

39 

40 . 

.003144 

• • • • 

.007 

.005 

.0048 

.0045 

40 


j 





















































APPENDIX 


229 


“Code” Wire and Cords 

The grade of wire and cord used in most indoor electric 
light and power work is known as “Code.” These wires 
and cords are made in accordance with the requirements 
of Underwriters’ Laboratories which inspects and tests 
them as they are made at the wire factories. 

Such “approved” products may be identified by the 
Laboratories’ labels found on the tags attached to the 
coils of rubber-covered wire, fixture wire and flexible 
cords. The labels on armored cable are placed around 
the armor about every fifty feet. 

The Laboratories have a large inspection force and are 
continuously making inspections at factories throughout 
the country, authorizing the use of labels on materials 
that conform to the standard requirements. The label 
is thus a valuable asset to the purchaser and user, indicat¬ 
ing as it does that the material has been inspected and 
tested by an entirely disinterested inspection force and 
that its quality is up to standard. Labeled products are 
not necessarily uniform in quality or merit, but at least 
they all meet certain minimum requirements necessary 
for protection against fire. 

Each manufacturer uses a marking of a thread or group 
of threads by means of which his product may be identi¬ 
fied. The Underwriters’ Laboratories List of Inspected 
Electrical Appliances gives the list of manufacturers of 
“Code” wire with the marking used by each. Copies of 
the List may be obtained in most cities from the Labora¬ 
tories’ office or from the local insurance inspector. 

“Approved Fittings” 

Only fittings which have been tested and listed by Un¬ 
derwriters’ Laboratories should be used in electric light 
and power work. Nearly all standard wiring devices are 
submitted by their makers for such tests and listing so 


230 


APPENDIX 


that the choice available is very large and there is little 
excuse for using others. The use of approved fittings is 
required by all insurance inspectors and by most city in¬ 
spectors as well. 

All of these approved fittings, or “listed” fittings, as they 
are called by the Laboratories, have been carefully in¬ 
vestigated as to their fire hazard. Only those devices are 
listed which are found by test to be built in a reasonably 
safe manner, so that when properly installed they are 
unlikely to cause fire from overheating, arcing or defective 
insulation. 

Copies of the Laboratories’ List may be obtained from 
the Laboratories’ offices and from inspection departments. 

BROWN & SHARPE’S GAUGE. 

The B. & S. Gauge is standard for copper wire and is understood 
to apply in all cases where size of copper wire is mentioned in any 
wire gauge number. 

By referring to the table it will be seen that in the B. & S. gauge, 
for all practical purposes, the area in circular mils is doubled for every 
third size heavier, by gauge number, and halved for every third size 
lighter, by gauge number. 

Every tenth size heavier by gauge number has ten times the area 
in circular mils. 

No. io B. & S. gauge wire has an area of approximately 10,000 
circular mils, and from this base the other sizes can be figured, if a 
table should not be at hand. 


CLASSIFICATION OF GAUGES. 

In addition to the confusion caused by a multiplicity of wire 
gauges, several of them are known by various names. 

For example: 

Brown & Sharpe (B. & S.) = American Wire Gauge (A. W. G.). 

New British Standard (N. B. S.) = British Imperial, English 
Legal Standard and Standard Wire Gauge and is variously abbre¬ 
viated by S. W. G. and I. W. G. 

Birmingham Gauge (B. W. G.) = Stubs, Old English Standard 
and Iron Wire Gauge. 

Roebling = Washburn Moen, American Steel & Wire Co.’s Iron 
Wire Gauge. 

London = Old English (Not Old English Standard). 

As a further complication: 

Birmingham or Stubs’ Iron Wire Gauge is not the same as Stubs’ 
Steel Wire Gauge. 


APPENDIX 


231 


GENERAL USES OF VARIOUS GAUGES. 

B. & S. G.—All forms of round wires used for electrical conduc¬ 
tors. Sheet Copper, Brass and German Silver. 

U. S. S. G.—Sheet iron and steel. Legalized by act of Congress, 
March 3, 1893. 

B. W. G.—Galvanized iron wire. Norway iron wire. 

American Screw Co.’s Wire Gauge.—Numbered sizes of machine 
and wood screws, particularly up to No. 14 (.2421 inch). 

Stubs’ Steel Wire Gauge.—Drill rod. 

Roebling & Trenton.—Iron and steel wire. Telephone and tele¬ 
graph wire. 

N. B. S.—Hard drawn copper. Telephone and telegraph wire. 

London Gauge.—Brass wire. 


EQUIVALENTS OF WIRES: B. & S. GAUGE. 


0000 

= 

2-0 

— 

4-3 

= 

8-6 

= 

16-9 

000 

= 

2-1 

= 

4-4 

= 

8-7 

= 

16-10 

00 

= 

2-2 

= 

4-5 

= 

8-8 

= 

16-11 

0 

= 

2-3 

= 

4-6 

= 

8-9 

= 

16-12 

I 

= 

2-4 

= 

4-7 

== 

8-10 

= 

16-13 

2 

= 

2-5 

= 

4-8 

= 

8-11 

= 

16-14 

3 

= 

2-6 

= 

4-9 

= 

8-12 

= 

16-15 

4 

= 

2-7 

= 

4-10 


8-13 

= 

16-16 

5 

= 

2-8 

= 

4-11 

= 

8-14 

= 

16-17 

6 

= 

2-9 

= 

4-12 

= 

8-15 

= 

16-18 

7 

= 

2-10 

= 

4-13 

= 

8-16 



8 

== 

2-11 

= 

4-14 

= 

8-17 



9 

= 

2-12 

= 

4-15 

= 

8-18 



10 

= 

2-13 

= 

4-16 





11 

= 

2-14 

= 

4-17 





12 

= 

2-15 

= 

4-18 





13 

= 

2-16 

= 

4-19 





T/l 

— 

2—17 







1 4 









T e 

—• 

2—l8 







1 0 

16 

= 

2-19 








32-12 = 64-15 
32-13 = 64-16 
32-14 = 64-17 

32-15 . 

32-16 . 

32-17 . 

32-18 . 


OHM’S LAW. 

The Electrical Units—Volt, ohm and ampere, which are most 
frequently used, have fortunately been established so as to bear 
simple but important relations to one another, based upon the cur¬ 
rent increasing and decreasing with the voltage, but increasing when 
the resistance decreases, and decreasing when the resistance increases. 

Using the Symbols mentioned above, this is expressed in the 
following equations: 

E E 

I =- E = I. R. R =- E. I. (or watts) = l 2 R. 

R C 

E 2 

E. I. (or watts) =- 

R 



































232 


APPENDIX 


ELECTRICAL UNITS. 

l t 

The electrical units are derived from the following mechanical 
units of the metric system: 

Centimeter. Unit of Length—One thousand millionth part of a 
quadrant of the earth’s surface. 

Gramme. Unit of Weight—Weight of a cubic centimeter of 
water at a temperature of 4 degrees centigrade. 

Second. Unit of Time—The time of one swing of a pendulum 
making 86,400 swings in a solar day. 

The unit of area is the square centimeter. The unit of volume is 
the cubic centimeter. 

Volt —Unit of electro-motive force; pressure of potential. Sym¬ 
bol E. 

Ohm —Unit of resistance. Symbol R. 

Megohm —1,000,000 ohms. 

Ampere —Unit of current. Symbol I. 

Ampere Hours —Current in amperes X time in hours. 

Watt —Unit of power. Product of 1 volt X 1 ampere. Symbol 
W. or E. I (746 watts equal one horsepower). 

Horsepower —746 watts. 

Kilowatt —1000 watts. Written K. W. 

Kilowatt Hours —Kilowatts X time in hours. 

Farad —Unit of capacity. 

Microfarad —One-millionth of a farad. Written M. F. 

Coulomb. Unit of Quantity—Quantity of current which, im¬ 
pelled by one volt, would pass through one ohm in one second. 

Joule. Unit of Work—The work done by one watt in one second. 


MILS AND CIRCULAR MILS. 

The one-thousandth part of one inch, written .001, and usually 
called one mil, is taken as the unit of diameter, from which one square 
mil would be the unit of area. If you measure the diameter of a 
round wire in thousandths of an inch, or mils, by means of a microme¬ 
ter, and multiply this number by itself, i.e., square it, you obtain in 
square mils the cross-sectional area of a square wire having four 
sides, each the same length as the diameter of the round wire that 
you have calipered. 

Circular mil (usually written C. M.) applies to all round wires, 
and has a value . 785 times that of the square mil. 

Consequently the square of the diameter of any round wire, 
measured in mils, gives its cross-sectional area in circular mils, with¬ 
out any further multiplication. 

Conversely, if you extract the square root of the number of cir¬ 
cular mils, by which a round wire is listed, you obtain its diameter 
in mils. 



APPENDIX 


233 


ELECTRICAL UNITS AND MECHANICAL EQUIVALENTS. 

AMPERES PER HORSEPOWER. 

The following table shows number of amperes required per horse¬ 
power when the percentage of efficiency of the motor is known. 

Efficiency of Motor 75 Per Cent 80 Per Cent 85 Per Cent 90 Per Cent 

At 110 Volts. . . . 9 Amp. 8.4 Amp. 7.9 Amp. 7.5 Amp. 

At 220 Volts. .. . 4.5 Amp. 4.2 Amp. 3.95 Amp. 3.75 Amp. 

At 500 Volts. ... 1.98 Amp. 1.86 Amp. 1.75 Amp. 1.66 Amp. 


AMPERES PER GENERATOR. 


K. W. 

125 Vs. 

250 Vs. 

500 Vs. 

Appx. H. 

I . 

8 

4 

2 

i -3 

2. 

16 

8 

4 

2.7 

3 .• 

24 

12 

6 

4.0 

5 . 

40 

20 

10 

6.7 

7-5 . 

60 

30 

15 

10. 

10. 

80 

40 

20 

13. 

12.5. 

100 

50 

25 

17. 

15 . 

120 

60 

30 

20. 

20. 

160 

80 

40 

27. 

25 . 

200 

100 

50 

3 • 

30 . 

240 

120 

60 

40. 

37-5 . 

300 

150 

75 * 

50 . 

40 . 

320 

160 

80 

53 * 

50 . 

400 

200 

100 

67. 

60. 

480 

240 

120 

80. 

75 . 

600 

300 

150 

100. 

100. 

800 

400 

200 

134 . 

i25. 

1000 

500 

250 

167. 

150. 

1200 

600 

300 

201. 

200. 

1600 

800 

400 

268. 













I 


234 


APPENDIX 


AMPERES PER MOTOR. 



Per Cent 

Watts 

SO 

100 

220 

500 

H. P. 

Eff. 

Input. 

Volts. 

Volts. 

Volts. 

Volts. 

3 x£ . 

70 

800 

16 

7 

4 

2 

iH . 

70 

1600 

32 

15 

7 

3 

3 . 

75 

2980 

60 

27 

14 

6 

5 . 

80 

4660 

93 

42 

21 

9 

7 y A . 

85 

6580 

132 

60 

30 

13 

10 . 

85 

8780 

176 

80 

40 

18 

15 . 

85 

13200 

264 

120 

60 

26 

20 . 

85 

17600 

352 

160 

80 

35 

25 . 

85 

21900 

438 

199 

100 

44 

30 . 

9° 

249OO 

498 

226 

113 

50 

40 . 

90 

332OO 

664 

301 

151 

65 

50 . 

90 

414OO 

828 

376 

188 

83 

60 . 

90 

49700 

994 

452 

226 

99 

70 . 

90 

58000 

1160 

527 

264 

116 

80 . 

90 

663OO 

1330 

603 

302 

133 

90 . 

90 

74600 

1490 

678 

339 

149 

100 . 

90 

82900 

1660 

755 

377 

166 

120 . 

90 

99500 

1990 

905 

453 

199 

150 . 

90 

I24OOO 

2480 

1130 

564 

248 


I 

HP 

E 

K 


I = 


Current in Amperes. 
Horsepower. 

Voltage. 

Efficiency of Motor. 
HP X 74600 

E X K 





















APPENDIX 


235 


WIRE DATA 


DIMENSIONS AND RESISTANCES OF COPPER WIRES. 


B. & S. 

Diameter 
in Mils or 

Area in 

Ohms 

Lbs. Per 

Gauge No. 

Thousandths 

Circular 

Per 

1,000 Ft. 


of an Inch. 

Mils. 

10,000 Ft. 

W. P. Ins, 


1,000 

894 

1,000,000 

.OIO38 

3,550 


800,000 

. OI297 

2,880 


775 

600,000 

.OI73 

2,210 


707 

500,000 

.02076 

1,875 


632 

400,000 

.02596 

1,530 


548 

300,000 

.0346 

LI85 

OOOO. 

460 

211,600 

.O4906 

750 

OOO. 

410 

167,805 

.06186 

600 

00. 

365 

133,079 

.07801 

500 

O. 

325 

105,592 

.0983 

400 

I. 

289 

83,694 

. I240 

300 

2. 

258 

66,373 

52,633 

.1564 

250 

3 . 

229 

.1972 

200 

4 . 

204 

41,742 

.2487 

160 

5 . 

182 

33,102 

.3136 

I40 

6. 

162 

26,250 

• 3955 

no 

8. 

128 

16,509 

. 6288 

75 

10. 

102 

10,381 

1. 

50 

12. 

81 

6,530 

1.590 

35 

14 . 

• • • 

4,107 

2.591 

25 

16. 

5 i 

2,583 

4.019 

16 

18. 

40 

1,624 

6.391 

12 


GALVANIZED IRON WIRE—WEIGHT AND RESISTANCE 

CALCULATED AT 68° F. 



Iron Wire 

Diameter 

Pounds 

/—Ohms Resistance Per Mile- 


Gauge. 

in Mils. 

Per Mile. 

E. B. B. 

B. B. 

Steel. 

4 - 



730 

6.44 

7-53 

8.90 

6. 


. 192 

540 

8.70 

10.19 

12.04 

8. 


. 162 

380 

12.37 

14.47 

17.IO 

9 - 


. 148 

320 

14.69 

17.19 

20.31 

10. 


•135 

260 

18.08 

21.15 

25.OO 

11. 


. 120 

214 

21.96 

25.70 

30.37 

12. 


•105 

165 

28.48 

33-33 

39-39 

14. 


.080 

96 

48.98 

57.29 

67.71 
































APPENDIX 


2x6 


FINE MAGNET WIRE 

, —Ohms, Per Pound—\ r ~ —Feet, Per Pound 


No. B. & S. 
Gauge. 

Diameter. 

Single 

Cotton. 

Double 

Cotton. 

Single 

Cotton. 

Double 

Cotton. 

20. 

. .0319 

3 -i 5 

3.02 

311 

298 

21. 

.0284 

4-97 

4.72 

389 

370 

22. 

• .0253 

7.87 

7-44 

491 

461 

23 . 

. .0225 

12.45 

11 .7 

624 

584 

24. 

.0201 

I 9-65 

18.25 

778 

745 

25 . 

. .0179 

30.9 

28.45 

958 

903 

26. 

• .0159 

48.5 

44-3 

1188 

1118 

27 -... 

.OI42 

76.5 

68.8 

1533 

1422 

28.. 

.0126 

120. 

106.5 

1903 

1759 

29 . 

.0112 

190.5 

164. 

2461 

2207 

30 . 

.OIOO 

294-5 

252. 

2893 

2534 

31 . 

.OO89 

461. 

384-5 

3483 

2768 

32 . 

. OO79 

717 - 

585- 

4414 

3737 

33 . 

. 0070 

1115. 

880. 

5688 

4697 

34 . 

. OO63 

I 7 I 5 - 

I 3 I 5 - 

64OO 

6168 

35 . 

. OO56 

2640. 

i960. 

8393 

6737 

36 . 

. .005 

4070. 

2890. 

9846 

7877 

37 . 

. OO44 

6180. 

4230. 

H636 

9309 

38 . 

. .OO39 

9430 . 

6150. 

13848 

10666 

39 . 

• -0035 

14200. 

8850. 

18286 

11907 

40 . 

. .0031 

21300. 

12500. 

24381 

14222 


RUBBER COVERED WIRE—SOLID CONDUCTORS 


■Single Braid—s' 1 ,—Double Braid—\ 


Size 

Diam. of 

Capacity 

Diam. 

Weight 

Diam. 

Weight 

B. & S. 

Conductors, 

Circular, 

Over 

Per 

Over 

Per 


Mils. 

Mils. 

All. 

1,000 Ft. 

All. 

i.ooo Ft. 

*0000. 

... 460 

2Il600 

47/64 

809 

55 64 

832 

OOO. 

... 410 

167803 

Il/l6 

666 

13/16 

690 

OO. 

• •• 365 

133079 

5/8 

546 

47/64 

568 

O. 

■ • • 325 

105524 

19/32 

453 

45/64 

476 

I. . . . 

. . 289 

83695 

33/64 

355 

5/8 . 

376 

2. 

••- 258 

66373 

29/64 

275 

9 /i 6 

295 

3 . 

,.. 23O 

52634 

2-7/64 

227 

33/64 

245 

4 . 

... 204 

41743 

25/64 

186 

15/32 

200 

5 . 

182 

33102 

23/64 

160 

7/16 

170 

6. 

162 

26250 

5/16 

128 

25/64 

135 

8. 

129 

16510 

17/64 

80 

n/32 • 

86 

10. 

... 102 

IO382 

15 64 

58 

19/64 

64 

12. 

8l 

6530 

7/32 

43 

9/32 

48 

14 . 

64 

4107 

13/64 

32 

i /4 

37 

16. 

• - 51 

2583 

3/16 

20 



18. 

, . . 40 

1624 

11/64 

16 



19 . 

36 

1288 

5/32 

15 


• • ® 

20. 

• - • 32 

1022 

9/64 

14 


■ 1 • 












































APPENDIX 


237 


DATA ON SOLID WIRES LARGER THAN 4/0 


No. B. & S. 

Diameter, 

Circular 

Feet Per 

Pounds Ohms. Per 

Gauge. 


Mils. 

Mils. 

Pound. Per Foot. 

Mile. 

5/0. 


515 

265,225 I 

.29 

.80 

.206 

6/0. 


575 

330,625 I 

.00 

I .00 

.165 

7/0. 


640 

409,600 

.81 

I.24 

•133 

8/0. 


710 

504,100 

.66 

i-53 

. 108 

9/0 . 


785 

616,225 

•54 

1.86 

.089 

10/0. 


865 

748,225 

•44 

2.25 

.073 

11/0. 


950 

902,500 

•37 

2-73 

.060 

12/0. 


1040 

1,081,600 

.21 

3-27 

.050 


STRANDED CONDUCTORS. 




Concentric 








Strands 

Diam. of 


—Single Braid—• 

—Double Braid — 

Size B. & S. — 

-- 


Conduc- 

Diam. 

Weight 

Diam. 

Weight 


No. 

Diam. 

tors, 

Over 

Per 

Over 

Per 

Wires. 

Each. 

Mils. 


All. 1 

,000 Ft. 

All. 1,000 Ft. 

2000000 C.M. 

91 

148 

'1650 

2 


7246 

2 9/64 

7385 

1750000 C.M. 

91 

139 

1550 

I 

29/32 

6394 

2 3/64 

6525 

1500000 C.M. 

91 

128 

1430 

I 

51/64 

5539 

I 15/16 

5658 

1250000 C.M. 

91 

117 

1308 

I 

43/64 

4678 

I 13/16 

4783 

1000000 C.M. 

6l 

128 

Il66 

I 

1/2 

3754 

1 5/8 

3849 

900000 C.M. 

6l 

12 I 

IIO4 

I 

7/16 

3404 

I 9/16 

3491 

800000 C.M. 

6l 

115 

IO49 

I 

3/8 

3058 

I l/2 

3138 

750000 C.M. 

6l 

III 

1013 

I 

II/32 

2881 

I 15/32 

2956 

700000 C.M. 

6l 

107 

978 

I 

5/l6 

2709 

I 7/16 

2880 

650000 C.M. 

6l 

103 

943 

I 

17/64 

2534 

I 25/64 

2600 

600000 C.M. 

6l 

99 

906 

I 

l/4 

2355 

I 3/8 

2418 

550000 C.M. 

6l 

95 

870 

I 

13/64 

2182 

I 21/64 

2240 

500000 C.M. 

37 

116 

821 

I 

1/8 

1959 

I 1/4 

2010 

450000 C.M. 

37 

no 

779 

I 

3/32 

1791 

I 7/32 

I84O 

400000 C.M. 

37 

104 

738 

I 

3/64 

1608 

I II/64 

1650 

350000 C.M. 

37 

97 

688 

I 


I43i 

I l/8 

I468 

300000 C.M. 

37 

90 

639 


I5/l6 

1250 

I l/l6 

1285 

250000 C.M. 

37 

82 

583 


7/8 

1071 

I 

1103 

0000 

19 

.105 

530 


13/16 

899 

I5/l6 

942 

000 

19 

.094 

475 


3/4 

740 

7/8 

782 

00 

19 

.083 

425 


45/64 

607 

13/16 

647 

0 

19 

.074 

380 


5/8 

492 

47/64 

526 

1 

19 

.066 

329 


9/16 

387 

43/64 

417 

2 

19 

.059 

296 


1/2 

303 

39/64 

329 

3 

7 

.086 

263 


29/64 

249 

9/16 

272 

4 

7 

.077 

233 


7/16 

204 

17/32 

227 

5 

7 

.068 

209 


13/32 

175 

1/2 

192 

6 

7 

.061 

185 


3/8 

141 

29/64 

156 

8 

7 

.048 

147 


21/64 

90 

13/32 

IO3 

10 

7 

.039 

118 


19/64 

65 

3/8 

72 

12 

7 

.031 

94 


17/64 

48 

21/64 

55 

14 

7 

.024 

75 


15/64 

36 

19/64 

40 











238 


APPENDIX 


RUBBER COVERED DUPLEX. 

,-Solid-\ ,-Stranded- 


Size B. & S. 

Diameter 
Over All. 

Weight Per 
1,000 Ft. 

Diameter 
Over All. 

Weight Per 
1,000 Ft. 

I. 


• • • 

I 1/4 

8lO 

2. 



I 1/8 

638 

3 . 



I 1/32 

528 

4 .. 



31/32 

442 

5 . 



29/32 

375 

6. 


. . 1 

53/64 

307 

8. 

. Il/l6 

170 

49/64 

203 

10. 

• 37/64 

125 

5/8 

143 

12. 

l/2 

94 

9/16 

107 

14 . 

. 27/64 

73 

15/32 

78 


All Weights are Approximate but are Exact Enough for all 
Practical Purposes. 


COPPER FOR VARIOUS SYSTEMS OF DISTRIBUTION. 

Power transmitted, distance, line loss and voltage of lamps con¬ 
stant. All wires of each system, same size. 

System. Copper Required. 


2- Wire, single-phase or direct current.-.. .. 1.000 

3- Wire, single-phase or direct current. -375 

4- Wire, single-phase or direct current.222 

4-Wire, two-phase. 1.000 

4-Wire, three-phase with neutral.333 

3-Wire, three-phase Delta.75 


j 































APPENDIX 239 

TABLE 1. TWO-WIRE AND THREE-WIRE SYSTEMS 


\ 


Size of 
Conductor 


Number of Conductors 

in One Conduit 


1 

2 

3 

4 

5 

6 

7 

8 

9 

B. & S. Gage 

14. 

•• X 

k 

Minimum Size of Conduit in Inches 

X X X 1 1 1 

I 

12. 

.. x 

X 

X 

X 

X 

I 

1 

I 

T-X 

IO. 

• • X 

X 

X 

I 

I 

I 


iX 

tX 

8. 

• • Vi 

X 

I 

I 

I 

tX 

T-X 

iK 

T-X 

6. 

.. yt 

I 

iX 

*x 

tX 

tX 

2 

2 

2 

5. 

.. X 

*x 

iX 

T-X 

tX 

2 

2 

2 

2 

4. 

.. X 

T-X 

iX 

T-X 

2 

2 

2 

2 

2^ 

3. 

.. X 

*x 

iX 

T-X 

2 

2 

2 

2K 

2^ 

2 . 

.. X 

1 X 

*x 

T-X 

2 

2 

2^ 

2 X 

2"X 

1 . 

.. X 

1 X 

*x 

2 

2 

2^ 

2^ 

z 

z 

0. 

. . I 

t-X 

2 

2 

2 X 

2~X 

3 

3 

3 

00. 

. > I 

2 

2 

2~X 

2X 

3 

3 

3 

3X 

000. 

. . I 

2 

2 

2 X 2 

z 

3 

3 

3 K 

3X 

0000. 

■ • i X 

2 

2 X 2 

2 X 2 

3 

3 

ZX 

3 K 

A 

200000 C. M .. . . 

■ • *X 

2 

2 X 2 

3 

3 

3 

zX 

3 ^ 

A 

225000. 

• • i X 

2 X 

2 X 

3 

3 

zX 

3 X 

4 

A 

250000. 

•. *X 

2 X 2 

2 X 

3 

3 

3X 

3 l X 

4 

aX 

300000. 

.. iX 

2 X 2 

z 

3 

3 K 

3X 

A 

4 >< 

aX 

35000°. 

• • iX 

2 X 2 

3 

zX 

zX 

A 

4 A 

4 >^ 

5 

400000. 

• • iX 

3 

3 

3 X 

A 

4 

4 A 

5 

5 

450000. 

• . 1 x 

3 

3 

3 X 

A 

4 A 

4A 

5 

6 

500000. 

.. 1 x 

3 

3 

zX 

A 

4 ^ 

5 

5 

6 

550000. 

.. iX 

3 

zX 

A 

4A 

5 

5 

6 

6 

600000. 

. . 2 

3 

zX 

A 

4'A 

5 

6 

6 

6 

650000. 

. . 2 

3 K 

3X 

A 

4 A 

5 

6 

6 

6 

700000. 

. . 2 

zX 

3X 

4 A 

5 

5 

6 

6 


750000. 

. . 2 

zX 

3X 

4A 

5 

6 

6 

6 


800000. 

. . 2 

zX 

4 

4A 

5 

6 

6 

6 


850000. 

. . 2 • 

zX 

4 

4'A 

5 

6 

6 



900000. 

. . 2 

zX 

4 

4A 

5 

6 

6 



950000. 

. . 2 

4 

4 

5 

6 

6 

6 



1000000. 

. . 2 

4 

4 

5 

6 

6 




1100000. 

.. 2^ 

'4 

4 A 

6 

6 




. ... 

1200000. 

.. 2 X 

4 A 

aX 

6 

6 





1250000. 

.. 2X 

4'A 

4'A 

6 

6 


/ * * 



1300000. 

.. 2~X 

4'A 

5 

6 

6 





1400000. 

.. 2^ 

aX 

5 

6 






1500000. 

.. 2^ 

4 yi 

5 

6 






1600000. 

.. 2^ 

5 

5 

6 




N 


1700000. 

• • 3 

5 

5 

6 






1750000. 

• • 3 

5 

5 

6 






1800000. 

• • 3 

5 

6 

6 






1900000. 

• • 3 

5 

6 







2000000. 

• • 3 

5 

6 

.. . 




































































240 


APPENDIX 


SIZE OF CONDUITS FOR THE INSTALLATION OF 
WIRES AND CABLES 

The following tables apply only to complete conduit systems and 
do not apply to short sections of conduit used for the protection of 
exposed wiring from mechanical injury. 

For sizes not greater than No. io B. & S. gage, one more conductor 
than permitted by the opposite table may be installed in-the specified 
conduit provided the conduit is not longer than 30 feet, and has not 
more than the equivalent of two quarter bends from outlet to outlet, 
the bends at the outlets not being counted. 


TABLE 2. THREE CONDUCTOR CONVERTIBLE SYSTEM 



Size of Conductors 

Size Conduit, In. 


B. & S. Gage 

Electrical Trade Size 

two 

14 

and one 

10. 

. X 

u 

12 

U 

8. 

. X 

a 

10 

u 

6. 


u 

8 

u 

4 . 



6 

u 

2. 

. *X 


5 


1. 

. iX 


4 


0. 

. i X A 


3 


00. 

. 1 A 


2 


000. 



I 


0000. 



0 


250000. 



00 


350000. 



000 


400000. 

. 2^ 


0000 


550000. 



250000 

u 

600000. 



300000 

u 

800000. 



400000 


1000000. 

. 3 'A 


500000 


1250000. 



600000 

u 

1500000. 



700000 


1750000. 



800000 


2000000. 



The following table must not be used for other than Stage Pocket 
and Border Circuits, except by special permission of the Inspection 
Department having jurisdiction. 


TABLE 3. STAGE POCKET AND BORDER CIRCUITS 


Size of 

Maximum Number of Conductors in 

Conduit 

Conductor 

Ins. 

Ins. 

Ins. 

Ins. 

Ins. 

Ins. 

B. & S. Gage 

1 

*X 

IX 

2 


3 

14. 


19 

26 

43 

61 

95 

12. 


15 

21 

34 

50 

77 

10. 


12 

l6 

27 

38 

60 

8. 

A 



13 

22 

31 

49 

O.. 



• • 

• • 

14 

22 


For groups or combinations not included in the above tables, 
consult the Inspection Department having jurisdiction. For such 
groups or combinations, it is recommended that the conduit be of 
such size, that the sum of the areas of the several conductors will 
not be more than 40 per cent, of the area of the conduit. 




























APPENDIX 


241 


USEFUL TABLES 
THE METRIC SYSTEM 
WEIGHTS. 


Equivalents in Denominations in 
Metric Denominations and Values. Use—Weight of What Quantity of 

Name. No. Grams. Water at Maximum Density. 


Millier or tonneau 

= 

1,000,000 

= 

i cubic meter. 

Quintal 

= 

100,000 

_« 

1 hectoliter. 

Myriagram 

= 

10,000 

= 

10 liters. 

Kilogram or Kilo 

— 

1,000 

= 

1 liter. 

Hectogram 

= 

100 

= 

1 deciliter. 

Dekagram 

= 

10 

= 

10 cu. centimeters. 

Gram 

= 

1 

= 

1 cu. centimeter. 

Decigram 

= 

. 1 

= 

. 1 cu. centimeter. 

Centigram 

= 

.01 

= 

10 cu. millimeters. 

Milligram 

= 

.001 

= 

1 cu. millimeter. 

Name. 


No. Grams. 


Avoirdupois Weight. 

Millier or tonneau 

= 

1,000,000 

= 

2,204.6 pounds. 

Quintal 

= 

100,000 

= 

220.46 pounds. 

Myriagram 

— 

10,000 

— 

22.046 pounds. 

Kilogram or Kilo 

= 

1,000 

= 

2.2046 pounds. 

Hectogram 

= 

100 

= 

3.5274 ounces. 

Dekagram 

= 

10 

= 

0.3527 ounce. 

Gram 

= 

I 

= 

15.432 grains. 

Decigram 

= 

. I 

= 

1.5432 grains. 

Centigram 

= 

.01 

= 

0.1543 grain. 

Milligram 

= 

.001 

= 

0.0154 grain. 


MEASURES OF LENGTH. 

= 10,000 meters = 6.2137 miles. 

= 1,000 meters = 0.62137 m. or 3,280 ft. 10 in, 

= 100 meters = 328 ft. and 1 inch. 

= 10 meters = 393.7 inches. 

= 1 meter = 39.37 inches. 

= . 1 of a meter = 3-937 inches. 

=* .01 of a meter = 0.3937 inch. 

= . 001 of a meter = o. 0394 inch. 


MEASURES OF SURFACE. 

Hectare = 10,000 sq. meters = 2.471 acres. 

Are = 100 sq. meters = 119.6 sq. yards. 

Centare = 1 sq. meter = 1,550 sq. inches. 


Myriameter 

Kilometer 

Hectometer 

Dekameter 

Meter 

Decimeter 

Centimeter 

Millimeter 


242 


Name No. 

Kiloliter 

Hectoliter 

Decaliter 

Liter 

Deciliter 

Centiliter 

Milliliter 

Name No. 

Kiloliter 

Hectoliter 

Decaliter 

Liter 

Deciliter 

Centiliter 

Milliliter 

Unit. 


I H. P. 


i H. P. Hour = 


I Kilowatt = 


1 APPENDIX 

MEASURES OF CAPACITY. 


Liters. 


Cubic Measure 


Dry Measure 

1,000 

= 

i cubic meter 

= 

i. 308 cu. yds. 

100 

= 

. 1 cubic meter 


2 bu. 3.35 pks. 

10 

= 

10 cu. decimeters 

= 

9.08 quarts. 

I 

= 

1 cu. decimeter 

— 

0.908 quart. 

. I 

= 

. 1 cu. decimeter 

= 

6.1022 cu. ins. 

.01 

= 

10 cu. centimeters 

= 

0.6102 cu. in. 

.001 

= 

1 cu. centimeter 

= 

0.061 cu.in. 

Liters. 


Cubic Measure 


Wine Measure 

1,000 

= 

I cubic meter 

= 

264.17 gals. 

100 

= 

. 1 cubic meter 

= 

26.417 gals. 

10 

= 

10 cu. decimeters 

= 

2.6417 gals. 

I 

= 

1 cu. decimeter 

= 

1.0567 quarts. 

. I 

= 

. 1 cu. decimeter 

= 

0.845 gill 

.01 

=: 

10 cu. centimeters 

= 

0.388 fluid oz. 

.001 

= 

1 cu. centimeter 

= 

0.27 fluid oz. 


Equivalent Value in Other Units. 

746 watts. 

. 746 K. W. 

33,000 ft.-lbs. per minute. 

550 ft.-lbs. per second. 

2,545 heat-units per hour. 

42.4 heat-units per minute. 

. 707 heat-unit per second. 

. 175 lb. carbon oxidized per hour. 

2.64 lbs. water evaporated per hour from 
and at 212 0 F. 

746 K. W. hours. 

1,980,000 ft.-lbs. 

2,545 heat-units. 

273,740 k. g. m. 

. 175 lb. carbon oxidized with perfect 
efficiency. 

2.6 4 lbs. water evaporated from and at 
212 0 F. 

17.0 lbs. water raised from 62° to 212 0 F. 
1,000 watts. 

1.34 H. P. 

2,654,200 ft.-lbs. per hour. 

44,240 ft.-lbs. per minute, 
v 737-3 ft.-lbs. per second. 

3,412 heat-units per hour. 

56.9 heat-units per minute. 

. 948 heat-unit per second. 

.2275 lb. carbon oxidized per hour. 

3.53 lbs. water evaporated per hour from 
and at 212 0 F. 






APPENDIX 


243 


1 Watt per 
sq. in. 


8.19 heat units per sq. ft. per minute. 
• 6,371 ft.-lbs. per sq. ft. per minute. 
k .193 H. P. per sq. ft. 


1 Kilogram 

Metre 


’ 7.233 ft.-lbs. 

.00000365 H. P. hour. 
.00000272 K. W. hour. 
. 0093 heat-units. 


1 lb. Water 
Evaporated 
from and 
at 212 0 F. 


.283 K. W. hour. 

• 379 H. P. hour. 

965.7 heat-units. 

103,900 k. g. m. 

1,019,000 joules. 

751,300 ft.-lbs. 

. 0664 lb. of carbon oxidized. 


\ 

1 Heat-unit = 


’ 1,055 watt seconds. 

778 ft.-lbs. 

107.6 kilogram metres. 

.000293 K. W. hour. 

.000393 H. P. hour. 

. 0000688 lb. carbon oxidized. 

.001036 lb. water evaporated from and at 
212 0 F. 


1 Heat-unit 
per sq. ft. = 
per min. 


’ . 122 watts per sq. in. 

• .0176 K. W. per sq. ft. 
( .0236 H. P. per sq. ft. 


1 Watt 


1 joule per second. 

.00134 H. P. 

3,412 heat-units per hour. 

. 7373 ft.-lb. per second. 

.0035 lb. water evaporated per hour. 
Ad. 24 ft.-lbs. per minute. 


1 K. W. 
Hour 


1,000 ' watt hours. 

1.3 \ H. P. hours. 

2,654,200 ft.-lbs. 

3,600,000 joules. 

3,412 heat-units. 

367,000 kilogram metres. 

.235 lb. carbon oxidized with perfect effi¬ 
ciency. 

3.53 lbs. water evaporated from and at 
212 0 F. 

22.75 lbs. of water raised from 62 0 to 212 0 F. 










244 


APPENDIX 


i Joule 


i ft.-lb. • 


I lb. Car¬ 
bon Oxi¬ 
dized with 
Perfect 
Efficiency 


' i watt second. 

.000000278 K. W. hour. 

. 102 k. g. m. 

. 000947 7 heat-units. 

. -7373 ft.-lb. 

1 • 35b joules. 

.1383 k. g. ip. 

• .000000377 K. W. hours. 

.001285 heat-units. 

.0000005 H. P. hour. 

[ 14,544 heat-units. 

1.11 lb. anthracite coal oxidized. 

2.5 lbs. dry wood oxidized. 

21 cu. ft. illuminating gas. 

4.26 K. W. hours. 

5 . 7 i H. P. lours. 

11,315,000 ft.-lbs. 

15 lbs. of water evaporated from and at 
212 0 F. 


DECIMAL EQUIVALENTS. 

Df eighths,"sixteenths, thirty-seconds and sixty-fourths of an inch. 


Fractions 


Decimals 

Fractions 


Decimals 

Fractions 


Decimals 

of 


of 

of 


of 

of 


of 

an Inch. 


an Inch. 

an Inch. 


an Inch. 

an Iijch. 


an Inch. 

1/64 

= 

.015625 

II/32 

=3 

•34375 

43/64 

— 

.671875 

1/32 

= 

.03125 

23/64 

=3 

•359375 

Il/l6 

= 

•6875 

3 M 

= 

.046875 

3 / 8 

= 

•375 

45/64 

= 

.703125 

l/l6 

= 

.0625 

25/64 

= 

.390625 

23/32 

— 

.71875 

5/64 

= 

.078125 

13/32 

= 

.40625 

47/64 

= 

•734375 

3/32 

= 

•09375 

27/64 

= 

.421895 

3/4 

= 

•75 

7 M 

= 

• 109375 

7/16 

= 

•4375 

49/64 

= 

.765625 

1/8 

= 

.125 

29/64 

= 

•453125 

25/32 

= 

.78125 

9/64 

= 

.140625 

15/32 

= 

•46875 

51/64 

= 

.796875 

5/32 

— 

.15625 

31/64 

= 

.484375 

13/16 

= 

.8125 

11/64 

= 

.171875 

l/2 

= 

•5 

53/64 

= 

.828125 

3 /i6 

= 

.1875 

33/64 

= 

.515625 

27/32 

= 

.84375 

13/64 

= 

.203125 

17/32 

= 

.53125 

55/64 

— 

.859375 

7/32 

= 

.21875 

35/64 

= 

.546875 

7/8 

= 

•875 

15/64 

= 

.234375 

9/16 

= 

.5625 

57/64 

= 

.890625 

l /4 

= 

•25 

37/64 

= 

.578125 

29/32 

= 

.90625 

17/64 

= 

.265625 

19/32 

= 

•59375 

59/64 

= 

.921875 

9/32 

= 

.28125 

39/64 

= 

.609375 

15/16 

— 

•9375 

19/64 

= 

.296875 

5/8 

= 

.625 

61/64 

= 

.953125 

5 /i 6 

= 

.3125 

41/64 

= 

.640625 

31/32 

= 

.96875 

21/64 

= 

.328125 

21/32 

= 

.65625 

63/64 

= 

.984375 






APPENDIX 


245 


FEET EXPRESSED IN DECIMAL PARTS OF A MILE. 



Units. 

Tens. 

Hundreds. 

Thousands. 

I . 


.OOI893 

.OI893 

.1893 

2. 


.OO3787 

.03787 

•3787 

3 . 


.005681 

•.05681 

.5681 

4 . 

.OOO757 

.OO7574 

•07574 

•7574 

5. 


.OO9468 

.09468 

.9468 

6. 


.OII362 

.II362 


7 . 

.OOI325 

•013255 

.13255 


8. 


.015148 

.15148 


9 . 


.OI7042 

.17042 



GENERAL EQUIVALENTS. 


CM = Circular mils. 

SqM = Square mils. 

1 CM = . 7854 SqM. 

1 SqM. = 1.2732 CM. 

1 Sq. in. = 1,000,000 SqM. 


1 Sq. in. = 1,273,200 CM. 

1 Sq. in. = area of a circle 1.128" diam. 
Area of circle 1" diam. = 1,000,000 CM. 
Area of circle 1" diam. = 785,400 SqM. 


TABLE OF MULTIPLES. 

Diameter of a circle X 3.1416 = Circumference. 

Radius of a circle X" 6.283185 = Circumference. 

Square of the radius of a circle X 3.1416 = Area. 

Square of the diameter of a circle X 0.7854 = Area. 

Square of the circumference of a circle X 0.07958 = Area. 

Half the circumference of a circle X by half its diameter = Area. 
Circumference of a circle X 0.159155 = Radius. 

Square root of the area of a circle X 0.56419 = Radius. 
Circumference of a circle X 0.31831 = Diameter. 

Square root of the area of a circle X 1.12838 = Diameter. 
Diameter of a circle X 0.86 = Side of inscribed equilateral tri¬ 
angle. 

Diameter of a circle X 0.7071 = Side of an inscribed square. 
Circumference of a circle X 0.225 = Side of an inscribed square. 
Circumference of a circle X 0.282 = Side of an equal square. 
Diameter of a circle X o. 8862 = Side of an equal square. 

Base cf a triangle X by Y2 the altitude = Area. 

Multiplying beth diameters and .7854 together = Area of an 
ellipse. 

Surface of a sphere X by 1/6 of its diameter = Solidity. 
Circumference of a sphere X by its diameter = Surface. 

Square of the diameter of a sphere X 3.1416 = Surface. 

Square of the circumference of a sphere X 0.3183 = Surface. 
Cube of the diameter of a sphere X 0.5236 = Solidity. 

Cube of the radius of a sphere X 4.1888 = Solidity. 

Cube of the circumference of a sphere X 0.016887 = Solidity. 
Square root of the surface of a sphere X 0.56419 =* Diameter. 











24 6 


APPENDIX 


Square root of the surface of a sphere X i. 772454 = Circum- 
ference. 

Cube root of the solidity of a sphere X 1.2407 = Diameter. 
Cube root of the solidity of a sphere X 3.8978 = Circumference. 
Radius of a sphere X 1.1547 = Side of inscribed cube. * 

Square root of (1/3 of the square of) the diameter of a sphere = 
Side of inscribed cube. 

Area of its base X by 1 /3 of its altitude = Solidity of a cone or 
pyramid, whether round, square or triangular. 

Area of one of its sides X 6 = the surface of a cube. 

Altitude of trapezoid X Yl the sum of its parallel sides = Area. 


PULLEY TABLES. 

PULLEYS AND GEARS. 

For single reduction or increase of speed by means of belting 
where the speed at which each shaft should run is known, and one 
pulley is in place: 

Multiply the diameter of the pulley which you have by the num¬ 
ber of revolutions per minute that its shaft makes; divide this product 
by the $peed in R. P. M. at which the second shaft should run. The 
result is the diameter of pulley to use. 

Where both shafts with pulleys are in operation and the speed of 
one is known: 

Multiply the speed of shaft by diameter of its pulley and divide 
this product by diameter of pulley on the other shaft. The result 
is the speed of the second shaft. 

Where a countershaft is used, to obtain size of main driving or 
driven pulley, or speed of main driving or driven shaft, it is necessary 
to calculate, as above, between the known end of the transmission 
and the countershaft, then repeat this calculation between the 
countershaft and the unknown end. 

A set of gears of the same pitch transmits speeds in proportion to 
the number of teeth they contain. Count the number of teeth in 
the gear wheel and use this quantity instead of the diameter of pulley, 
mentioned above, to obtain number of teeth cut in unknown gear, 
or speed of second shaft. 


RULE FOR FINDING SIZE OF PULLEYS. 

D x S d x S' 

d = - D =- 

S' • S 

d = diameter of driven pulley. 

D = diameter of driving pulley. 

S = number of revolutions per minute of driving pulley. 
S' = number of revolutions per minute of driven pulley. 




GEAR TABLE—DIAMETRAL PITCH. (Nutt&T. 

Diametral Pitch is the Number of Teeth to Each Inch of the Pitch Diameter, 


APPENDIX 



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INDEX 


Alcohol torch, 25. 

Alternating current motors, 
188-197. 

classes of, 189-197. 
reversing, 192-193, 195-196. 
starting, 190-192, 193-195- 
wiring for, 188-189. 

Amperes, per generator, 233. 
per horse power, 233. 
per motor, 234. 

Annunciator, gravity drop, 
39 - 

needle, 42. 
return call, 42. 
simple, 41. 

Annunciator system, hotel, 
210-212. 
kitchen, 209. 

Annunciators, 30. 

Apartment house telephone 
system, 212. 

Appendix, 225-247. 

Armored cable, 127-132. 
cutting, 128. 
fixture outlets, 131. 

A 13 condulet, 107. 

Automatic burner, 45. 


Basement wiring, 93. 
Bathrooms and damp places, 
fittings for, 162. 

Battery systems, locating trou¬ 
ble in, 49. 

Bell-ringing transformers, 52. 
Bell, vibrating, 30. 

wiring, 34. 

Bells, 30-44. 


Bells, door, with annunciator, 
35 - 

extension, 216. 
in multiple, 36. 
in series, 36. 

Bending conduit, 111-113. 

Bit extensions, 3. 

Bits, 2. 

Blow torch, gasoline, 24. 
Bonding lengths, metal mold¬ 
ing, 135 - 

Boring floor joists, 87. 

Boring machines, 3. 

Box, “kicking,” 71-72. 

Boxes, cabinet, 62. 
miter, 4. 

Switch and cabinet, 62. 
Braces, 2. 

Branch circuits, 62, 87, 98. 
Britannia splice, 18. 

Brown & Sharpe’s gauge, 230. 
Building, entering the, 87, 98, 
107. 

Buildings, fireproof, 118. 
Burglar alarm system, closed 
circuit, 40. 
open circuit, 38. 

Burglar circuit, 158. 

Burner, automatic, 45. 
pendant, 44. 

Buzzer, two bells and, 36. 
“BX” in finished house, use of, 
127-128. 


Cabinet, wooden, 176, 177. 
Cabinet boxes, 62. 

Cable, armored, 127-132. 




249 




250 


INDEX 


Cable splice, taper, 19. 

Cable passing through parti¬ 
tions, 130-131. 
under floors, 129-130. 
securing, to boxes, 128. 

Capacity, measures of, 242.- 

Caution, telephone wiring, 206. 

Cellar or basement wiring, 93. 

Cells, charging, 52. 
gravity, 51. 

Leclanche, 50. 
renewing, 51. 

Central energy system, 221. 

Charging cells, 52. 

Chisels, 3. 

Circuit, burglar, 158. 
short, 162-164. 

Circuits, branch, 62, 87, 98. 
tap, 62. 

Circular mils, 232. 

Clamps, splicing, 5. 

Classes of alternating current 
motors, 189-197. 

Classification of gauges, 230. 

Closed-circuit burglar alarm 
system, 40. 

Code requirements, for mo¬ 
tors, 180-181. 
for telephone, 203-204. 

Combination squares, 4. 

Compound motors, 187. 
controlling speed of, 188. 
wiring of, 187. 

Concealed and open conduit, 
107. \ 

Concealed knob and tube wir- 
_ ing, 85-104. 
switches, 97. 
tests, 95. 

Concealed wiring, 31. 

Conductivities, 225. 

Conductivity, relative, 2^6. 

Conductors, 225. 
solid, 236. 
stranded, 237. 


Conduit, bending, m-113. 
concealed and open, 107. 
preparing for use, no. 
rigid, 107-124. 
sizes, 239. 

systems, grounding, 119. 
Conduits, fishing wires through, 
120-121. 

Condulet, A, 13, 107. 
Controlling speed of motors, 
186-188. 

compound motors, 188. 
Convertible system, three-wire, 
147-149. 

Copper for various systems of 
distribution, 238. 

Copper, soldering, 25. 

Copper wires, dimensions of, 
_ 235. 

resistances of, 235. 

Coppers, soldering, 5. 

Cords, drop, 67. 

Current required to fuse, 22), 
Cutters, molding, 5. 
pipe, 4. 

Cutting armored cable, 128. 
metal molding, 133-134. 


Damp places, 118. 

fittings for, 162. 

Data, wire, 235. 

“Dead end,” 63. 

Decimal equivalents, 244-245. 
Diagram, house, 59. 

Diametral pitch, 247. 

Dies, 4. 

Difference between wire 
gauges, 228. 

Dimensions of copper wires, 
235 - 

Direct current motors, 181-188. 

types of, 182-188. 
Distribution, copper for various 
systems of, 238. 





INDEX 


251 


Distribution, systems of, 146. 
Door bell, simple, 35. 

with annunciator, 35. 

Drills, 4. 
star, 3. 

Drop cords, 67. 

Dry Leclanche cells, 51. 
Duplex, rubber-covered, 238. 
Duties, of electrical contractor, 
166-167. 

of electrical supply firm, 166- 
167. 

of gas-fitter, 165. 
of power company, 165. 

Electric wiring, importance 
of, 1. 

Electrical contractor, duties of, 
166-167. 

Electrical supply firm, duties 
of, 166-167. 

Electrical units, 232. 
Electrician’s tools, 1. 

Electrolier switches, 158. 

'‘End, dead,” 58. 

Entering the building, 87, 98, 
107. 

Entering with mains, 61. 
Equivalent values, 242-244. 
Equivalents, decimal, 244-245. 
general, 245. 
of wires, 231. 

Extension bells, 216. 

Extensions, bit, 3. 


Files, 4. 

Final tests, 98, 102. 

metal molding, 140. 

Fine magnet wire, 236. 
Fireproof buildings, 118. 

Fish tape, 4. 

Fishing wires through con¬ 
duits, 120-121. 


Fittings for bathrooms and 
damp places, 162. 

Fixture outlets, 90. 

armored cable, 131. 

Fixture splice, 18. 

Fixtures, 64, 95, 101. 
rigid conduit, installing, 121- 
122. 

wiring, 48. 

Floor boards, removing, 100. 
Floor joists, boring, 87. 

Floor, wiring under a, 98. 
Floors, passing cable under, 
129-130. 
replacing, 102. 

Flush switches, 91, 100. 
Four-point switches, 152-153. 
Four-wire, two-phase lighting 
system, 149. 

Friction tape, tearing, 28. 

Fuse, current required to, 227. 

Galvanized iron wire, resist¬ 
ance of, 235. 
weight of, 235. 

Gas-fitter, duties of, 166. 

Gas lighting, 30, 44-54. 
multiple, 49. 
wiring for, 44. 

Gasoline blowtorch, 24 
Gauge, Brown & Sharpe’s, 230. 
Gauges, classification of, 230. 
difference between, 228. 
uses of, 231. 

Gear table, 247. 

Gears, 246. 

General equivalents, 245. 
Generator, amperes per, 233. 
Good ground, 47. 

instructions for making, 47. 
Good joint, requirements for, 
ir. 

Gravity cells, 51. 

Gravity drop annunciator, 42. 




INDEX 


Ground, good, 47. 

Grounding conduit systems, 
119. 

metal molding, 140. 


Hammers, 2. 

“Hickey,” 112. 

Horse power, amperes per, 233. 
Hotel annunciator telephone 
system, 210-212. 

House diagram, 9. 


Illumination, power required 
for, 174-176. 

Importance of electric wir¬ 
ing, 1. 

Important fittings, metal mold¬ 
ing, 136-137. 

Induction motor, 190. 

Inserting wires, 88. 

Inspection, 102. 

Installation, planning, 85. 

Installing fixtures, rigid con¬ 
duit, 122-123. 

Instructions for joints and 
splices, 12. 

for making a good ground, 
47 - 

Insulation of wire, 177. 

Insulators, 225. 

Intercommunicating telephone 
system, 212-213. 

Introduction, 1-7. 


Joint, loop tee, 15. 

Joint or splice, preparing wires 
for, 12. 
rat-tail, 17. 
tee, 15. 

Joints and splices, instructions 
for, 12. 
soldering, 23. 


Joints and splices, wire, 11. 
Joists, wires parallel to, 89. 

“Kicking” box, 71-72. 

Kitchen annunciator telephone 
system, 209. 

Knife switches, 173-174. 

Knob and tube wiring, con¬ 
cealed, 85-104. 


Law, Ohm’s, 231. 

Leclanche cells, 50. 
dry, 51. 
wet, 50. 

Length, measures of, 241. 
Lighting, gas, 30, 44 - 54 - 
multiple gas, 49. 

Lights, number of, 172-173. 
Lines, party, 217-221. 

Locating outlets, 173. 
trouble in battery systems, 
49 - 

troubles, 162-164. 

Loop tee joint, 15. 

Loops, meter, 150-151. 

Low voltage systems, sources 
of power for, 50. 

Lugs, soldering wires into, 26. 


Machines, boring, 3. 

Magnet wire, fine, 236. 

Mains, entering with, 61. 
size of, 167-172. 

Markings, wire, 229. 

Measures of capacity, 242. 
length, 241. 
surface, 241. 

Melting point, 226. 

Metal molding, 132-142. 
bonding lengths of, 135. 
cutting, 133-134. 
final tests, 140. 
grounding, 140. 



INDEX 


253 


Metal molding, important fit¬ 
tings for, 136-137. 
mitering, 137-138. 
passing through floors, 138. 
passing through partitions, 
139 . 

supports, 134-135- 
wires in, 132. 

Meter loops, 150-151. 

Meter, wiring for, no. 
Methods, time-saving, 66. 
Metric system, 241-242. 

Mils, 232. 

circular, 232. 

Miter boxes, 4. 

Mitering metal molding, 137- 
138. 

wood molding, 72-73. 
Molding cutters, 5. 

Molding, metal, 132-142. 
wood, 70. 

Motor, amperes per, 233. 

Motor generator sets, 53. 
Motor, induction, 190. 
series, 186, 190. 

alternating current, 190. 
shunt, 182-186. 

Motors, alternating current, 
188-197. 

code requirements for, 180- 
181. 

compound, 187. 
controlling speed of, 186. 
direct current, 181-188. 
synchronous, 197. 
wiring for, 180-199. 
wiring systems, 180. 
Mounting switches, 64. 
Multiple, bells in, 36. 

gas lighting, 49. 

Multiples, table of, 245-246. 


Needle annunciator, 42. 
Number of lights, 172-173. 


Offsets, 114. 

Ohm’s Law, 231. 

Open and concealed conduit, 
107. 

Open-circuit burglar alarm sys¬ 
tem, 38. 

Open circuits, tests for, 70. 

Open wiring, 59-103. 

Open work wiring, 32. 

Outlet boxes and fixtures, sup¬ 
porting, 116-117. 

Outlet for rigid conduit, 115- 
116. 

Outlets, fixture, 90. 
locating, 173. 


Partitions, passing cable 
through, 130-131. 

Parts, wood molding, 70. 

Party lines, 217-221. 

Passing cable through parti¬ 
tions, 130-131. 
under floors, 129-130. 

Passing metal molding through 
•v floors, 138. 

through partitions, 139. 
Pendant burner, 44. 

switches, 151. 

Pipe cutters, 4. 
vises, 4. 

Pitch, diametral, 247. 

Places, damp, 118. 

Planning installation, 85. 

Pliers, 2. 

Pockets, 99. 

Point, melting, 226. 

Power company, duties of, 166. 
Power for low voltage sys¬ 
tems, sources of, 50. 
Power required for illumina¬ 
tion, 174-176. 

Practice, wiring, 166-179. 
Preparing conduit for use, no. 
wires for joint or splice, 12. 





254 


INDEX 


Protectors, telephone, 204-205. 
Pulley tables, 246. 

Pulleys, 246. 


Rat-tail joint, 17. 

Reamers, 4. 

Receptacles, rosettes and, 63. 
Relative conductivity, 226. 
Remote control switches, 159- 
160. 

Removing floor boards, 100. 
Renewing cells, 51. 

Replacing floors, 102. 

Required tools, 61. 
Requirements, code, for mo¬ 
tors, 180-181. 
for a good joint, 11. 
Resistance of copper wires, 
235 - . ‘ 

galvanized iron wire, 235. 
Return call annunciator, 42. 
systems, 37. 

Reversing a motor, 192, 195. 

shunt motor, 184-186. 
Reversing alternating current 
motors, 192-193, 195-196. 
Rigid conduit, 107-124. 
outlet, 115-116. 
tests, 123. 

Rooms, wiring between, 63. 
Rosettes and receptacles, 63. 
Rule for size of pulleys, 246. 


Safety switches, 159-160. 

Saws, 3. 

Screw drivers, 2. 

Securing cable to boxes, 128. 
Series, bells in, 36. 

Series, motor, 186, 190. 
alternating current, 190. 
wiring of, 186. 

Sets, motor generator, 53. 
Short circuit, 162-164. 


Short circuit, tests for, 70-71. 
Shunt motor, 182-186. 

Simple annunciator, 41. 

door bell, 35. 

Size of mains, 167-172. 

pulleys, rule for, 246. 

Sizes, conduit, 239. 

Soldering copper, 25. 

tinning, 25. 

Soldering coppers, 5. 

Soldering joints, 23. 

wires into lugs, 26. 

Solid conductors, 236. 
wires, 237. 

Sources of power for low volt¬ 
age systems, 50. 

Special wiring, 143-165. 

Speed of motors, controlling, 
186, 188. 

Splice, Britannia, 18. 
fixture, 18. 
taper cable, 19. 
three-ply, 15. 

Western Union, 12. 

Splices, 11-28. 

Splicing clamps, 5. 

Squares, combination, 4. 
Stairway control systems, 156- 
158. 

Standard symbols for wiring 
plans, 6. 

wall sets, 213-216. 

Star drills, 3. 

Starting a shunt motor, 184. 
alternating current motors, 
190-192, 1 93 -1 95 - 
motor, 184, 190-192, 193-195. 
Stock and dies, 4. 

Stranded conductors, 237. 

wire, tee joint for, 20. 
Suggestions, switch, 151-154. 
Support for wood molding, 
7\- 

Supporting outlet boxes and 
fixtures, 116-117. 



INDEX 


oo 


Supports, metal molding, 134- 
135 - 

Surface, measures of, 241. 

Switch and cabinet boxes, 62. 

Switch and starting box, shunt 
motor, 183. 

Switches, 74-75. 
concealed knob and tube 
* wiring, 97. 
electrolier, 158. 
flush, 91, 100. 
four-point, 152-153. 
knife, 173-174- 
mounting, 64. 
pendant, 151. 
remote control, 159-160. 
safety, 159-160. 
suggestions, 151-154. 
tank, 160-161. 
three-point, 152. 

Symbols for wiring plans, 
standard, 6. 

Synchronous motors, 197. 

System, central energy, 221. 
four-wire, two-phase, 149. 
telephone, apartment house, 
212. 

hotel annunciator, 210-212. 
intercommunicating, 212-213. 

kitchen annunciator, 209. 
two-party, 207-208. 
three-wire, 147. 
convertible, 147-149. 

three-phase, 149. 
two-wire, 146-147. 

Systems of distribution, 146. 
return call, 37. 
stairway control, 156-158. 
telephone, 206-221. 

Tables, useful, 241-247. 
wiring, 225. 

Tank switches, 160-161. 

Tap circuits, 62. 


Tape, fish, 4. 

Taper cable splice, 19. 

Taping a wire joint, 27. 

Taps, 5. 

Tearing friction tape, 28. 

Tee joint, 15. 
for stranded wire, 20. 
loop, 15. 

Telephone, code rules, 203- 
204. 

protectors, 204-205. 
systems, 206-221. 
wiring, 205-206. 

Telephones, 203-223. 

Tests, 69-70, 95, 123. 
final, 98, 102, 123, 140. 
concealed knob and tube 
wiring,. 95. 
metal molding, 140. 
open circuits, 70. 
rigid conduit, 123. 
short circuits, 69-70. 
three-point and four-point 
switches, 154-156. 

Three - phase system, three- 
wire, 149. 

Three-ply splice, 15. 

Three-point and four-point 
switches, tests for, 154- 
156. 

Three-point switches, 152. 

Three-wire convertible system, 
147-149. 

Three-wire, three-phase sys¬ 
tem, 149. 

Three-wire system, 147. 

Time-saving methods, 66. 

Tinning soldering copper, 25. 

Tools, 6. 

electricians’, 1. 
required, 61. 
used, no. 

Torch, alcohol, 25. 

Torches, 5. 

Transformers, bell-ringing, 52. 




256 


INDEX 


Trouble in battery systems, 
locating, 49. 

Troubles, locating, 162-164. 
Tube wiring, concealed, 85- 
104. 

Two bells and buzzer, 36. 
Two-party system, telephone, 
207-208. 

Two-phase system, four-wire, 

149. 

Two-wire system, 146-147. 
Types of direct current mo¬ 
tors, 182-188. 


Units, electrical, 232. 

Use of “BX” in finished house, 
127-128. 

Useful tables, 241-247. 

Uses of gauges, 231. 

Values, equivalent, 242-244. 
Vibrating bell, 30. 

Vises, pipe, 4. 

Wall sets, standard, 213-216. 
Weight of galvanized iron 
wire, 235, 

Weights, 241. 

Western Union splice, 12. 

Wet Leclanche cells, 50. 

Wire data, 235-240. 
fine magnet, 236. 
insulation of, 177. 
joint, taping a, 27. 
joints, 11-27. 
markings, 229. 


Wires, equivalents of, 231. 
fishing through conduits, 120- 
121. 

in metal molding, 132. 
inserting, 88. 
into lugs, soldering, 25. 
parallel to joists, 89. 
soldering into lugs, 25. 
solid, 237. 

through conduits, fishing, 
120-121. 

Wiring, alternating current 
motors, 188-189. 
basement, 93. 
bell, 34. 

between rooms, 63. 
cellar or basement, 93. 
compound motor, 187. 
concealed, 31. 
fixtures, 48. 
gas lighting, 44. 
meter, no. 
motors, 180-199. 
open, 59-78. 
open work, 32. 
practice, 166-179. 
series motor, j 86. 
shunt motor, 183-184. 
special, 146-165. 
systems (motors), 180. 
tables, 225-229. 
telephone, 205-206. 
under a floor, 98. 

Wood molding, 70. 
mitering, 72-73. 
parts, 70. 
support for, 71. 

Wooden cabinet boxes, 176-177. 
Wrenches, 3. 


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